####018005298#### FXCA62 TJSJ 180910 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 510 AM AST Thu Apr 18 2024 .SYNOPSIS... Trofiness aloft will persist through next week; thus, afternoon convection due to local effects may result in thunderstorms across the interior and western sections. Any persistent moderate to locally heavy rain over the already saturated soils may result in river flooding or sudden mudslides along steep terrains this afternoon. A surface high-pressure migrating from the western Atlantic to the Central Atlantic from this weekend into next will promote an advective pattern from Sunday onward. && .SHORT TERM...Today through Saturday... Showers developed over Puerto Rico and the USVI throughout the early morning hours, with up to half an inch near Trujillo Alto and less elsewhere. Winds lightened and became variable with speeds around 3 mph at 4am this morning. Heavy rainfall yesterday caused Rio Grande de Manati and Rio Cibuco at Vega Baja to overflow their banks, causing flooding on the roads they intersect. Due to this Flood Warnings were issued until the morning. As the mid to upper-level and associated surface trough continue to pass through region unstable conditions will persist. By this morning, the surface trough has already moved past the USVI and due to it's positioning the surface winds will prevail from the NE today with light to moderate speeds, with stronger gust during the afternoon. By this afternoon the area will be under the stable side of the upper-level trough, however diurnal heating, local effects and lingering moist air will allow convection to bring heavy rainfall mainly across the interior to western sections of Puerto Rico. Due to previous days of heavy rainfall soils are already saturated which will increase the chance of runoff resulting in flash flooding and possible mudslides across areas with steep elevation. By tonight, conditions will begin to improve overall with the exiting of the upper-level trough and the mixing of drier air into the region as northerly winds prevail. A surface high begins to build in the western Atlantic, causing wind speeds to increase from the NE to N. Besides ongoing passing showers throughout the morning for northern and eastern PR and the USVI, Friday afternoon still holds a good chance to bring noticeable rainfall for southwestern to interior sections of Puerto Rico. A similar pattern will prevail on Saturday with southwestern Puerto Rico having the best chance of heavier rain. Temperatures are expected to be slightly cooler for northern coastal areas these days due to northerly wind. Again, for these days, flooding of small streams and urban areas remains totally possible with the heaviest activity mainly across the interior to western sections of PR during the afternoon hours. .LONG TERM...Sunday through Thursday... A surface high-pressure building north of the islands, promoting an advective pattern, will bring occasional moisture surges across the USVI and PR from Sunday onward. The winds will persist mainly from the east to east-northeast, which may result in the areas affected by passing showers being the islands' north and east windward sections, especially during the night and morning hours. These showers will bring periods of moderate to locally heavy rains at times. The afternoon convection will be driven mainly by local effects, diurnal heating, and sea breeze variations across the interior and western sections daily. Additionally, the latest model guidance suggests maximum temperatures near the normal climatological values during the long term. Around mid-week, an upper-level trough will approach from the west, increasing the local instability, which, combined with the sea breeze, orographic effects and diurnal heating could result in the typical strong afternoon convection of a wet April. && .AVIATION... (06z) VCSH are expected to continue across the local area through at least tonight. Periods of reduced VIS and low CIGs are possible during the afternoon with thunderstorm development. Winds are light and variable this morning and then will become NE at 10-15 kts aft 18/14z, with stronger gusts. && .MARINE... A set of surface troughs, one to the northwest and other to the northeast of the islands will promote light to locally moderate northeast winds today. A small northeasterly swell will move across the Atlantic water from today onward. The surface trough northeast of the region and a surface high pressure building across the western Atlantic will promote moderate to locally fresh trades by the weekend. && .BEACH FORECAST... A northeasterly swell, spreading across the local Atlantic, and the locally wind-seas will result in a moderate risk of rip currents along the north and east facing beaches in PR and the USVI. The northeasterly swell will continue throughout the weekend. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...RC LONG TERM....CAM ####018005970#### FXUS63 KDVN 180911 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 411 AM CDT Thu Apr 18 2024 .KEY MESSAGES... - Widespread chances of showers and a few thunderstorms will move through the area today, with perhaps a strong to severe storm or two for areas along and south of US Highway 34 this afternoon - Our first of several chilly nights develops tonight, with frost/freeze headlines likely needed at times through the weekend - Generally dry conditions expected throughout the long term period, with another system moving in for Monday night and Tuesday && .SHORT TERM /THROUGH TONIGHT/... Issued at 411 AM CDT Thu Apr 18 2024 After a quiet and calm early morning, we are now beginning to see light rain showers moving into our southwestern areas. This is associated with a large upper-level trough that is established across the far northwestern CONUS region. A mid-level shortwave is just starting to move in, along with a southerly 30 to 40 knot low-level jet nosing into our area. This activity will continue to expand over the next several hours. So far, there hasn't been any evidence of lightning, per the GOES-East GLM Flash Extent Density imagery. The latest HREF ensemble most- unstable CAPE progs indicate the instability gradient to remain to our south well into Missouri, although we could see some modest instability lifting northward this morning. The latest CAM guidance is suggesting that this morning's precipitation will be one of two rounds of showers and perhaps a few thunderstorms to move through our area today. The break in between these two rounds appears to occur right around noon before a second round moves in this afternoon. This second round appears to have more support for thunderstorms, thanks to stronger upward vertical motion and slightly higher surface dew points. If storms do develop, they are most likely south of Interstate 80. A tight baroclinic zone will also develop across our southeast this afternoon, which should establish frontogenetical forcing to help enhance lift. Instability is expected to remain quite modest this afternoon, but with the more favorable shear and aforementioned enhanced lift, storms could become more robust this afternoon with the second round. SPC continues to outline areas along and south of US Highway 34 in a Marginal Risk (level 1/5) for a severe storm or two, with large hail and locally strong winds as the main threats. A Slight Risk (level 2/5) remains just to our south. Pwat values between 1 to 1.50 inches will be maximized across our south, so most locations will see between 0.50 to 1.50 inches of rainfall in total with today's rain - a beneficial rainfall for those areas still impacted by drought. Precipitation from the second round will come to an end by this afternoon and early evening, leading to a dry and mostly calm night. We continue to watch our first potential for frost during the growing season tonight, and we have temperatures in the 30s forecast, coolest in northeastern Iowa. The window for frost potential is a bit short, mainly for after midnight tonight through sunrise, but winds are expected to quickly taper off during that time frame with clear skies, supporting frosty conditions. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Issued at 411 AM CDT Thu Apr 18 2024 Friday through Monday will see dry conditions. The main focus for this time frame will be a few chilly nights Friday, Saturday, and Sunday nights. Models suggest we will have zonal flow aloft, along with a large area of high pressure that will settle across the central CONUS. Confidence in frost Friday night/Saturday morning is a bit lower, as we will be contending with stronger winds and cloud cover in some parts of our area, which should inhibit radiational cooling/frost development. However, confidence is much higher for a freeze Saturday night/Sunday morning, with more ideal radiational cooling conditions. In fact, the NBM probabilities of low temperatures at or below freezing Saturday night/Sunday morning are between 70 to 100 percent across northeastern Iowa. Be on the lookout for any frost/freeze headlines issued this weekend! A mid-level shortwave is progged to move through the area Monday night and Tuesday. Per the GEFS and ECMWF ensemble low tracks, an attendant surface low will translate north of our region during that time, as it pulls some decent moisture northward. At this time, it appears to be mainly showers with perhaps some isolated storms with it. After the system passes through, dry conditions are likely to prevail through mid-week. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1249 AM CDT Thu Apr 18 2024 VFR under clear skies will be with us for at least a few hours as a surface high pressure ridge axis remains overhead. However, these quiet conditions will be short-lived as a system moves in from the west later on this morning and bring increasing chances of showers and storms, lingering through the afternoon hours today. Timing and intensity of the precipitation is a bit uncertain, given differences among the high-resolution models. However, it appears that there will be slightly better support for thunderstorms in the afternoon, especially for MLI and BRL, so used PROB30 groups to highlight when the most likely timeframe and impact for these storms will be. Overall, confidence is high for widespread MVFR/IFR conditions with this system. This activity moves out by tonight, leading to VFR. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...None. IL...None. MO...None. && $$ SHORT TERM...Schultz LONG TERM...Schultz AVIATION...Schultz ####018006272#### FXUS66 KOTX 180912 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 212 AM PDT Thu Apr 18 2024 .SYNOPSIS... Cool and showery conditions continue today, before drying out and becoming breezy Friday. Showers return for Saturday evening through Sunday. Mild and dry weather returns for the start of work week while showers arrive by mid week. && .DISCUSSION... Today through Saturday afternoon: Winds are light across the region tonight with cool temperatures. The likelihood of frost this morning remains over the Western Columbia Basin and Wenatchee area as clouds have eroded. A weak shortwave will move through the area, ushering in another bout of showers to northeast WA (perhaps even thunder - a 15% chance) and the ID Panhandle. Meanwhile, Eastern and Central Washington can expect partly to mostly sunny and dry conditions, though temperatures will remain cool in the 50s. Showers and winds will taper off in the evening. Moving into Friday, an upper-level low will traverse the region, tightening the pressure gradient and resulting in gusty winds across the Columbia Basin. Northeast winds will gust up to 35 mph in the afternoon before easing off overnight. Despite the windy conditions, temperatures will slightly warm up and the region will experience sunny weather. Dry and gusty conditions will lead to an elevated fire weather risk in dead grasses in the Columbia Basin. Looking ahead to Saturday, a ridge of high pressure will bring more sunny skies in the morning and temperatures in the 60s. An overcast cloud deck will move in Saturday afternoon bringing a 15% chance of showers to Stevens Pass Saturday afternoon. Winds will be breezy, gusting up to 30 mph across the region. /Butler Saturday night through Sunday night: There is good agreement of a negatively tilted upper level trough pivoting across the Pacific NW this weekend. Moisture spread east of the Cascades Saturday evening as a cold front marches across eastern WA into north ID during the overnight hours with chance of showers. Snow levels start high but lower to 3-4K ft by Sunday morning with light mountain snow accumulations. Breezy winds accompany the front Saturday night with wind gusts of 20-30 mph especially across the Columbia Basin and Palouse. In the wake of the front, surface based instability will promote afternoon convection especially across northeast WA and the ID Panhandle with a small chance of a thunderstorm near the BC border. Sunday will be a cool and brisk day. The westerly winds remain gusty across the Palouse into north ID Sunday afternoon. The showers and winds gradually dissipate Sunday evening. Monday through Tuesday: An upper ridge builds into WA on Monday while the upper level trough shifts east, although it still brushes the ID Panhandle. It will start off cool Monday morning with areas of frost across the lowlands of eastern WA. Temperatures on Monday warm to near seasonal levels by afternoon. Lingering moisture and surface based instability lead to the redevelopment of mountain showers over north ID. Winds will be lighter and shift from the east and temperatures rebound to more seasonal levels. The upper ridge shifts inland Monday night into Tuesday with light easterly winds and drier conditions. Daytime temperatures should mild on Tuesday with widespread 60s to lower 70s region-wide. Tuesday night through Thursday: Model guidance has lower confidence with the mid week forecast, especially dealing with how long the upper ridge remains and the timing of the next Pacific low pushing inland and at what trajectory. At least through Thursday, the position of the approaching trough remain near the coast to offshore which should keep a mild southwest flow into the region. The NBM begins to spread moisture and a chance of showers across the Inland NW by Tuesday night and continues a low chance of showers through Wednesday into Thursday. Temperatures look to remain on the mild side and just above seasonal normals with little in the way threat of freezing. /rfox. && .AVIATION... 06z TAFS: Convective clouds are dissipating across eastern WA and north ID. There are mid level clouds that are blossoming across central WA including MWH/EAT. These clouds will likely continue through the night and then clear towards mid to late morning. Showers will redevelop again Thursday afternoon, but confidence of them going over any particular TAF location is low. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence in VFR conditions through the TAF period. HREF is showing a 10-20% chance of MVFR conditions at COE from 09-16Z. NBM has about a 5% chance. Confidence of MVFR conditions developing is very low. ----------------------- Confidence descriptors: Low - Less than a 30 percent chance Moderate - 30 to 70 percent chance High - Greater than a 70 percent chance For additional probabilistic information for NWS Spokane airports, please refer to the Aviation Dashboard on our webpage: https://www.weather.gov/otx/avndashboard && .PRELIMINARY POINT TEMPS/POPS... Spokane 54 31 56 33 62 39 / 20 0 0 0 0 30 Coeur d'Alene 52 30 54 31 61 38 / 30 10 0 0 0 40 Pullman 53 31 56 33 62 38 / 10 0 0 0 0 40 Lewiston 61 34 64 36 69 44 / 10 0 0 0 0 40 Colville 54 27 57 27 63 35 / 30 10 0 0 0 40 Sandpoint 50 30 52 30 60 38 / 30 10 0 0 0 50 Kellogg 49 30 51 32 61 40 / 50 20 0 0 0 50 Moses Lake 62 36 64 38 67 41 / 0 0 0 0 0 10 Wenatchee 61 37 61 37 63 41 / 0 0 0 0 0 10 Omak 59 34 62 34 64 39 / 10 0 0 0 0 30 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Frost Advisory until 9 AM PDT this morning for Lewiston Area. WA...Frost Advisory until 9 AM PDT this morning for Lower Garfield and Asotin Counties-Moses Lake Area-Wenatchee Area. && $$