####018006770#### FXUS66 KMTR 040807 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 107 AM PDT Sat May 4 2024 ...New SYNOPSIS, SHORT TERM, LONG TERM... .SYNOPSIS... Issued at 1201 AM PDT Sat May 4 2024 A cold front will bring rain, strong winds, and much colder temperatures to the area today. A gradual warming trend will start Monday with dry weather and plenty of sunshine next week. && .SHORT TERM... (Today and tonight) Issued at 1201 AM PDT Sat May 4 2024 KMUX is starting to pick up on the main frontal rain band as it approaches the North Bay early this morning. To add timing precision, I used a blend of high-resolution short term models to create 1 hourly PoP grids. Based on the new official forecast, rain is expected to reach Santa Rosa by 4 AM, San Francisco by 6 AM, San Jose by 8 AM, and Salinas by 10 AM. The main band of rain should last 6-8 hours before tapering off. The expected total rainfall is continuing to tick up slightly, with 0.5-1.0" in most lowlands and 1.0-1.5" in the coastal mountains. Prefrontal SW winds are moderate this morning, but will increase to a strong breeze as the front approaches and switch to a NW direction after it passes. The confidence in the prefrontal stratiform rain described above is quite high, with very little ensemble spread. The bigger question today is if thunderstorms will develop in the cold, post frontal environment. The expected 700 mb temperature is near the daily minimum, which would suggest some instability, but there's a few complications. First, the coldest mid-level air doesn't settle in until Saturday night, after the surface temperature is on the down swing. Second, the 500 mb temperature is not as impressive as the 700 mb temperature with a more stable 3.5 C/km lapse rate between those two levels. This indicates any convection that initiates tomorrow will have a vertical limit of about 10,000 ft. With the top end of the hail growth zone (-30C) at over 22,000 ft, this limits the amount of ice that will be generated. The most likely scenario is that after the front moves through some isolated, low-topped convective showers will pop up through the evening. There is a scenario, however, where the skies clear after the front passes and the surface temperature increases more than expected. This could lead to some evening thunderstorms, particularly in the North Bay where the front will clear first and the potential surface heating is higher. To demonstrate this, I adjusted the NAM model sounding at Santa Rosa, increasing the surface temperature a few degrees to line up with our forecast of 13C/55.4F. This alone increased the CAPE from 130 J/kg to over 500 J/kg. If the surface temperature exceeds our expectations, the instability will be even higher. In other words, if the sun comes out in the afternoon, the chance for evening thunderstorms increases significantly. && .LONG TERM... (Sunday through Friday) Issued at 1201 AM PDT Sat May 4 2024 The cold front and associated low pressure system will clear the area by Sunday, leaving cold air in place. Sunday morning will be on the chilly side, with many inland areas dropping into the upper 30s or low 40s. There is a slight chance for some lingering showers on Sunday, but they should be isolated and on a decreasing trend through the day (if anything develops in the first place). Otherwise a gradual warming trend will kick off next week with Sunday highs in the 50s and 60s and Friday highs in the 70s and 80s. Expect lots of sunshine with breezy winds along the coast, especially during the first half of the week. && .AVIATION... (06Z TAFS) Issued at 942 PM PDT Fri May 3 2024 MVFR/IFR level clouds are moving inland. Winds are reducing and are expected to become light to moderate, then slowly turn to become more S/SW ahead of the approaching low pressure system. By the mid morning, most terminals will see winds increase once more to become breezy and gusty out of the SW, and rain begins, lowering visibilities at terminals. Cloud decks are expected to improve to lift slightly as the rain approaches. Rain continues into Saturday afternoon before dissipating, with winds turning to W/NW and becoming breezy. Expect these breezy winds to last into Saturday night. Vicinity of SFO...IFR and breezy into the night. Winds reduce further into the night and turn southwesterly. These winds become gusty as the rain arrives early Saturday morning with MVFR CIGs and slight reductions in visibility. Winds turn to become W/NW in the later morning, but rain lasts through the afternoon. VFR returns behind the rain band, with breezy westerly winds. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...IFR/LIFR CIGs last through the majority of the overnight hours with lighter winds. As the rain band arrives, expect CIGs lift to become IFR/MVFR late Saturday morning. Gusty westerly winds build along the rain band. VFR returns behind the main rain band with breezy winds easing into the late night. && .MARINE... (Tonight through next Thursday) Issued at 907 PM PDT Fri May 3 2024 Expect breezy to gusty northwest winds to continue with gale force gusts possible over the southernmost zones. This evening, a low pressure system and associated cold front will arrive from the north, bringing rain and moderate to fresh breezes across the waters. Winds will turn briefly southwesterly ahead of the system early Saturday morning, but turn to become northwesterly once more in the late part of Saturday morning. Rain ceases late in the day Saturday, and winds ease to become moderate into the new workweek. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM-SF Bay N of Bay Bridge. Small Craft Advisory from 9 AM this morning to 9 PM PDT this evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm. Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Pt Arena to Pt Reyes 0-10 nm. Gale Warning until 9 AM PDT this morning for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...Murdock MARINE...Murdock Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea ####018003530#### FXUS62 KKEY 040809 AFDKEY Area Forecast Discussion National Weather Service Key West FL 409 AM EDT Sat May 4 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 314 AM EDT Sat May 4 2024 High pressure remains centered near Bermuda and reaches southwest into the Gulf of Mexico. East winds at the Reef average 15 to 20 knots, similar to last night at this time. If this was a couple months from now the Straits of Florida would be speckled with nocturnally enhanced showers. The latest KBYX scans note just a few showers, likely due to the very dry profile (PW ~1.0") sampled by the 00Z KKEY RAOB. Temperatures are in the upper 70s across the island chain, a few degrees below the nearshore SSTs in the lower 80s. It does not feel too bad outside right now with dewpoints near 70. .FORECAST... Water vapor imagery highlights a mid to upper level low digging equatorward through eastern Cuba. The center of the mean layer ridging is displaced to the west of Central America, although 500 mb heights near the Yucatan are near 590 dm. The upper low will remain near or east of the Keys today through Tuesday night. This will prevent the deep mean layer ridge from sliding east. By Wednesday or Wednesday night, the mean layer ridge will progress to the east and finally kick the upper low deeper into the North Atlantic. Per the sensible weather elements, moderate to fresh easterly breezes will persist for the next several days. Shallow undulations in low-level moisture will maintain slim rain chances. As the upper low lifts north through Cuba and meanders near the Keys Sunday night through Monday night, the low level moisture may deepen somewhat. We continue to highlight 20% chances for this time frame, which is above climo and the MOS consensus. As the mean layer ridge takes hold around mid-week, slightly diminished breezes will take on more of an east-southeast fetch. Low-level moisture depth will be suppressed to below 900 mb. Forecast soundings suggest near nil rain chances, but we leaned on climo and held onto the 10% chances into the extended. Fans of humidity will be cheering as dewpoints return to the mid to upper 70s by next weekend :| && .MARINE... Issued at 314 AM EDT Sat May 4 2024 There are no watches, warnings, or advisories currently in effect for the coastal waters of the Florida Keys. High pressure over the western North Atlantic will maintain moderate to fresh easterly breezes for the next several days. Breezes will tend to peak overnight, followed by lulls in the afternoon. && .AVIATION... (06Z TAFS) Issued at 314 AM EDT Sat May 4 2024 VFR conditions will prevail at the EYW and MTH terminals through Saturday evening, with rain chances remaining very low. Brief MVFR ceilings around 2500 feet will be possible, mainly during the predawn and early morning hours. Surface winds will remain from the E to ESE at 10 to 15 knots, with gusts of 15 to 20 knots at times. && .PRELIMINARY POINT TEMPS/POPS... Key West 85 78 85 77 / 10 10 10 20 Marathon 85 78 85 77 / 10 10 10 20 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...CLR Aviation/Nowcasts....Jacobson Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest ####018007377#### FXUS64 KFWD 040809 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 309 AM CDT Sat May 4 2024 ...New Long Term... .SHORT TERM... /Issued 1214 AM CDT Sat May 4 2024/ /Overnight through Sunday/ Convection is waning across the region tonight as surface based inhibition increases. A cluster of showers and a few storms continue to the south of Waco at this hour, but this activity should diminish over the next hour or so. The remainder of the night should be quiet with light winds and humid conditions. Some patchy fog may develop later tonight into the early morning hours on Saturday. The active weather pattern will continue with a cold front currently across southwest Kansas expected to move through Oklahoma overnight and approaching North Texas Saturday morning. Synoptic scale forcing for ascent may be negligible during this time, but forcing along the front itself may be sufficient for scattered showers/storms to develop earlier than they did on Friday. This activity is most likely to occur across our northwest counties and generally north of I-20 into the early afternoon. We'll have some 30-40% PoPs to account for this activity while our central TX counties will likely remain dry. It's a little unclear whether or not the front will actually make it down into our area through midday with a consensus of the guidance suggesting that it'll get hung up to our north in response to an approaching upstream shortwave. This shortwave is evident on water vapor imagery approaching northern Baja California at this hour. Meanwhile, either an outflow boundary or just a general backing of the low level flow ahead of the front will likely lead to increased low level moisture convergence across the I-20 corridor through the afternoon. This will support isolated/scattered storm development through late afternoon, especially from the Metroplex westward. Meanwhile, thunderstorms will increase in coverage across West Texas and become severe near the intersection of the southward moving front and dryline late this afternoon. This activity will likely evolve into one or more clusters of thunderstorms and spread eastward into North Texas late Saturday night as stronger forcing for ascent from the aforementioned shortwave overspreads the Southern Plains. While there will certainly be some potential for severe weather, especially across our western counties, widespread heavy rainfall may result in additional flooding issues across parts of the region. Latest HREF guidance shows a large swath of 2-3 inches of rain through late Saturday night across our southwest counties, the majority of which falls in about 3 hours. This may necessitate a westward expansion of the flood watch. We'll coordinate this over the next several hours. Showers and thunderstorms will overspread much of the region late Saturday night and continue to move eastward into early Sunday morning, tapering off from west to east through the day. Additional thunderstorm development may occur late Sunday afternoon across our central and southeast counties as the front stalls in wake of the departing shortwave. Dunn && .LONG TERM... /NEW/ /Sunday Night Through Next Saturday Afternoon/ Thunderstorms may be ongoing at the start of the period, but convection will be weakening and should completely dissipate late Sunday evening. By early next week, the upper level low evident in current mid-level water vapor satellite imagery near the coast of the Pacific Northwest will eject across the central and northern Plains as an increasingly negatively tilted upper trough. As stronger height falls spread east toward the Rockies, surface low pressure will be generated enhancing southerly low-level flow and moisture advection across the southern Plains on Monday. While large-scale ascent attendant to the upper trough will largely be displaced to the north (OK/KS), favorable low-level moisture/instability ahead of an eastward mixing dryline may be sufficient for the development of isolated dryline-induced convection Monday afternoon. Given that convective coverage is likely to be low due to the presence of a capping inversion, PoPs have been capped at 30% Monday afternoon and evening. Instability in excess of 3000 J/kg MUCAPE and 35-50 kts of deep-layer shear should sustain any updrafts that develop. Large hail, localized severe gusts, and a tornado or two will be possible. Tuesday into Wednesday, the upper-level trough/low will linger over Montana and the Dakotas while upper-level ridging builds eastward across the Gulf Coast states. Amid south to southwest flow at the surface and quasi-zonal flow aloft, abnormal but sub- record heat is expected each afternoon through Thursday with highs in the mid 80s to lower 90s. This is near the 99th percentile of the historical temperature distribution for early May (according to NAEFS and ECMWF). A shortwave trough will begin working around the base of the slowly evolving northern Plains upper trough/low on Wednesday. The enhancement of mid-level flow along with strong instability ahead of the lingering dryline is expected to bring thunderstorm chances back into parts of North and Central Texas Wednesday afternoon and evening. Any thunderstorms that develop could become severe with all hazards possible. Storm chances will likely increase again on Thursday afternoon as the stalled surface cold front over Kansas finally begins pushing through Oklahoma and North TX providing a focus for additional convective development. In the wake of the departing trough/front, Mother's Day weekend is shaping up to be seasonably mild with highs in the mid 70s. 12 && .AVIATION... /Issued 1214 AM CDT Sat May 4 2024/ /6Z TAFs/ VFR cigs generally prevail in the wake of convection earlier this evening but conditions will again deteriorate overnight with MVFR cigs expected by morning across most of North and Central Texas. We'll be watching a front slide southward through the morning hours into the D10 airspace. This may be sufficient for a few isolated storms to develop earlier than they did on Friday. Better storm chances will arrive late Saturday night as another complex of storms is expected to track across North Texas through the overnight hours. Dunn && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 80 67 79 69 83 / 40 100 30 20 30 Waco 80 66 78 68 82 / 30 100 40 20 20 Paris 80 65 75 65 81 / 40 70 80 20 30 Denton 80 64 77 66 82 / 40 100 30 10 30 McKinney 80 66 76 67 82 / 40 90 40 20 30 Dallas 82 67 79 68 83 / 40 90 30 20 30 Terrell 80 67 78 67 82 / 40 90 40 20 20 Corsicana 82 68 79 69 84 / 30 90 40 20 20 Temple 81 67 79 69 82 / 30 90 40 20 10 Mineral Wells 79 64 79 66 84 / 40 100 10 20 30 && .FWD WATCHES/WARNINGS/ADVISORIES... Flood Watch through Sunday afternoon for TXZ135-146>148-160>162- 174-175. && $$