####018007620#### FXUS61 KPBZ 252143 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 543 PM EDT Thu Apr 25 2024 .SYNOPSIS... Mostly dry weather and a warming trend is expected through Monday save chances of isolates showers or storms Saturday and Sunday afternoon. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... KEY MESSAGES: - Freeze warnings and frost advisories are in effect for portions of the area, beginning at midnight. ------------------------------------------------------------------ Made some minor adjustments to sky cover and hourly temps/dewpoints for the next several hours, but there have been no major changes to the forecast thinking. Clouds have become more cellular and have started to dissipate as diurnal heating and mixing start to decrease. The overnight temperature forecast remains the same for now, and will reevaluate over the next few hours whether frost/freeze headlines need any adjustments. Previous discussion... Mundane weather will persist as the area sits underneath a subsidence inversion in a weak pressure gradient. For this reason, winds are expected to remain calm to light through the near term. A weak 850mb meso-low has been observed across southwest Pennsylvania, allowing weak low-level convergence and moisture pooling in the area just south of I-80. This has allowed stratocumulus decks to persist for much of the day as mixing has attempted to erode them. The current thinking is that most cumulus will dissolve with sunset, but patches of stratocumulus may linger in the aforementioned area overnight. Low- probability clouds are also possible in the Laurels with upsloping. Areas that are clear at this point will likely remain clear and there is a high probability that low temperatures tonight will under-perform guidance, thus, adjusted towards the NBM 10th percentile with calm winds. Should clouds linger a bit longer, temperature will likely run higher than the forecast. Frost advisories were hoisted based on the areal extent of 36 degrees or lower across a forecast zone after adjusting nocturnal temperatures down. The same goes for freeze warnings; there is a high probability of a freeze for Forest, and a moderate probability of a freeze for Venango, Clarion, and Jefferson PA. In these zones, calm winds and clear skies are high probability. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... KEY MESSAGES: - Dry and warmer through Friday - Showers and possible thunderstorms return Friday night into Saturday with a warm front ---------------------------------------------------------------- The surface high pressure will migrate to the east for Friday, with mostly clear skies for much of the daytime hours. As surface southeast flow accelerates with pressure gradient increases, temperatures will bounce above normal once again. Friday evening and overnight, clouds will increase as cirrus decks advect overhead. Thereafter, a warm front will progress through. Precipitation timing and amounts have trended slower and lower since the last update. Fumes of elevated instability are possible, thus a rumble of thunder could not be ruled out as it passes through Saturday morning. Even the 90th percentile is only around 0.25 inches of QPF. A moisture and temperature push is expected behind the warm front, with a chance of isolated afternoon showers and/or thunderstorms. Precipitation chances taper overnight. Because of the passing warm front from the west, daytime highs will range from above average in eastern Ohio to near/below average in central Pennsylvania. && .LONG TERM /SUNDAY THROUGH THURSDAY/... KEY MESSAGES: - Warm with minimal chances of afternoon thunderstorms Sunday and Monday. - More widespread showers and possible thunderstorms with a Tuesday cold front. ------------------------------------------------------------------- Model ensembles continue to indicate the strongest riding across the Upper Ohio Valley region Sunday and Monday. Sunday should be mainly dry under the ridge, with warm air aloft limiting convective potential. Still, an isolated afternoon storm or two is possible, mainly north of Pittsburgh, where another vort max moves across southern Ontario on the northern periphery of the ridge. Similar conditions are expected Monday. The ridge axis is expected to shift slowly eastward later Monday, with slightly better chances for afternoon showers and thunderstorms late in the day as a shortwave trough and associated surface cold front begin to approach from the Midwest. Temperatures mainly in the 80-85 degree range (outside of the higher terrain) are expected Sunday and Monday with a 1000-500 mb height of 582 dm, and 850 mb temperatures ranging from 12-14 deg C. Cooler, but still above average, temperatures should return Tuesday behind the front. Showers are likely, along with a few thunderstorms, on Tuesday as the trough and cold front cross the region. The precipitation should end Tuesday night as the front exits. By Wednesday, one thing is more certain; the ridge amplitude will decrease. Clustered variability of the 500mb pattern sits anywhere between a weak 500mb trough to a weak 500mb ridge. This ridge breakdown may lean towards more unsettled weather. Late next week, a central CONUS ridge may develop (shown in 3 out of 4 clusters). Should it develop, it is favored to move east (as shown in 2 out of 3 clusters) and allow warmer-than- normal temperatures to continue through next weekend. Some alternate scenarios include 1) the ridge not developing, whereby temperature would remain closer to normal in zonal flow and 2) the ridge develops but does not move east and enforces eastern troughing, which would keep temperatures below normal. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... Stratocumulus continues across a significant portion of the forecast area early this afternoon while ceilings have generally lifted to low-end VFR (3-5kft). Some erosion is beginning to take place along the southern border of this cloud deck per latest visible satellite imagery as MGW/ZZV have scattered out to mostly sunny skies. This trend should continue through the rest of the day with most of these clouds clearing by late evening, though some patches of scattered/broken coverage may linger into overnight hours. Winds are light across the area and should remain that way through the night before a strengthening and better established southeast flow sets up after 12Z Friday. .Outlook... VFR conditions are expected Thursday and Friday. The probability of showers and isolated thunderstorms increases Friday night into Saturday which will come with increasing probabilities for restrictions as well. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...Frost Advisory from midnight tonight to 9 AM EDT Friday for PAZ007-013-014-020-022-077-078. Freeze Warning from midnight tonight to 9 AM EDT Friday for PAZ008-009-015-016. OH...Frost Advisory from midnight tonight to 9 AM EDT Friday for OHZ039>041-048>050-057>059-068-069. WV...Frost Advisory from midnight tonight to 9 AM EDT Friday for WVZ001. && $$ SYNOPSIS...Milcarek NEAR TERM...CL/Milcarek SHORT TERM...Milcarek LONG TERM...WM/Milcarek AVIATION...Cermak ####018008923#### FXUS66 KPDT 252143 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 243 PM PDT Thu Apr 25 2024 .SHORT TERM...Today through Sunday...Current radar is showing the leading edge of the upper level trough has begun to push along the Cascades and spill over to the east slopes. Current observations show 0.01 inches along the OR east slopes and 0.01-0.03 inches along the WA east slopes. Current satellite shows mid and high level clouds over the majority of the CWA. This will assist with keeping temperatures more on the seasonal side. However, if there is a break in the clouds this afternoon, daytime heating coupled with some orographic lift and mid level moisture, the eastern mountains could hear a rumble or two of thunder this afternoon. Today through Friday night models are in relatively firm agreement with the upper level trough moving slowly across the region. With it there are elevated probabilities of some high mountains snow and low elevation rain. Looking at the raw ensembles 6 hour potential for 0.05 inches of rain, there is and 80-95% chance along the Cascades crests and along the east slopes of the Cascades through tonight while only a 5-15% chance along the eastern mountains, while the lower elevations will see a 30-40% chance of 0.01-0.06 inches of rain. Snow levels will decrease from over 5000 ft to near 4500 ft allowing the crests of the Cascades and portions of the Wallows to see an 80-90% probability of 0.5 inches along the Cascades and higher at the crests while the Blues and Wallowas have 60-80% probabilities for 0.5 inches as well. Along the OR Cascades through Santiam Pass there is a 30% probability of up to 3 inches. Not enough to warrant an advisory but still enough to say be cautious while driving across. As for the temperatures, due to the increased cloud cover, temperatures will remain near seasonable with the EFI showing seasonable temperatures and the ensembles showing low to mid 60s along the lower elevations and high 50s elsewhere. With the majority of the cloud cover currently over the eastern portion of the CWA, there is a slight chance with low confidence (5-15%), that the daytime heating coupled with a lifted index of above 6.5°C/km and MUCAPEs of 150J/kg, the eastern mountains could here a rumble or two this afternoon. CAMs models show these ingredients to uptick Friday afternoon to MUCAPEs of over 200 J/kg, lifted index cresting 7.4°C/km, mid level moisture and southwest flow, isolated thunderstorms could pop up over the eastern mountains Friday afternoon with confidence slightly higher (15-25%). Saturday the models show the upper level trough to have its axis over the region with the backside of the trough over the Cascades and the leading side over the eastern mountains. Guidance shows the majority of the precipitation will linger along the Cascades as well as the northern Blue Mountains and the Wallowas. With temperatures above freezing overnight and snow levels above 5000ft, much of the precipitation that will fall will be rain at pass levels and rain snow mix along the crests with 20-40% chances of up to 0.10 inches of rain. EFI continues to show the temperatures at seasonable with temperatures increasing ever so slightly to the upper 60s to low 70s through the lower elevations and mid to upper 50s elsewhere. Lastly, winds through the period will be west to southwest with a diurnally driven increase. Ensembles show high confidence (70-90%) that sustained winds will be 10-20 mph through the Cascade Gaps and along the lower Columbia Basin daily through Saturday and decreasing overnight. Bennese/90 .LONG TERM...Sunday through Thursday...The long term period is expected to see unsettled weather as a trough will be over the area through most of next week and a series of weak and moisture deprived fronts bring light amounts of rain mainly to the mountains. Temperatures will be generally near to slightly below normal for late April. There are growing differences between model ensemble members over time so while the overall pattern is clear, the finer details are less certain. The Extreme Forecast Index indicates little in the way of unusual weather aside from elevated winds Sunday and Monday afternoons in the Columbia Basin (EFI = 0.75-0.80). Models start out in good agreement on Sunday in having a strong upper low off the northern British Columbia coast and a shallow trough centered off the Pacific Northwest coast. A weak front and a generally west to southwest flow into the Cascades will bring a 60- 80 percent of rain along the Cascade crest with amounts of about a tenth of an inch or less. The northern portions of the eastern mountains will have a 20-35 percent chance of very light rain. Snow levels will be around 4500-5500 feet. The main concern will be winds with the frontal passage and 15-30 mph westerly winds are expected over most of the area in the afternoon. Temperatures will be slightly warmer than Saturday with highs in the upper 50s to mid 60s with 50s in the mountains. For Monday, models are still in reasonable agreement though model ensemble clusters show some differences. 70 percent of model ensemble members have the upper low over Vancouver Island or southern British Columbia though they have significant differences about the strength of the closed low. The other 30 percent have the low offshore near central British Columbia. They also indicate some form of weak front crossing the area in the afternoon with a 40-60 percent chance of light rain in the Cascades and a 15-25 percent chance in the eastern mountains. Amounts will be mainly just a few hundredths of an inch. The front will again bring some breezy westerly winds of 15-25 mph in the afternoon. Temperatures will be 3- 5 degrees cooler in the afternoon. At this point, model ensemble members diverge significantly. On Tuesday and Wednesday, 55 percent of the members have the upper low and trough centered off of Vancouver Island and the other 45 percent favor a shallower trough and low centered over Montana. The National Blend of Models favors the solution with the trough off the coast, though with pops of 20-40 percent in the Cascades and 15-25 percent in the eastern mountains with the rest of the area dry. Rain amounts will be minimal. The version with the trough offshore gives us a southwest flow which pumps up a ridge off to our east, which will warm temperatures a few degrees each day reaching the mid 60s to lower 70s with upper 50s to mid 60s in the mountains on Wednesday. It should be noted that the 25th percentile and 75th percentile of temperatures have a broad range of 10-15 degrees, so forecasted temperatures have low confidence. For Thursday, 62 percent of the models continue to keep a strong trough along the Pacific Northwest coast and a strong ridge over the Midwest with a southwest flow over our area while the others show a weak trough developing along the coast or just ashore and a weaker ridge over the midwest. Both solutions favor rain, so have a 40-60 percent chance of rain over the mountains and a 15-30 percent chance over the lower elevations. The mountains will get up to a tenth of an inch of rain while amounts will be very light in the lower elevations. The trough and greater precipitation and cloudiness will cool temperatures to the 60s with 50s in the mountains. Temperature spread remains wide and confidence remains low. Perry/83 && .AVIATION...(Previous Discussion)...18Z TAFS...VFR are currently favorable for most sites, but MVFR conditions for KBDN due to low CIGs and VSBY this afternoon until VFR again tonight. Due to the arrival of the cold front moving over PacNW, rain and wind gusts become the highlight for this TAF period. Winds will be moderate at 10-15 kts for sites KBDN/KYKM/KPSC through morning/afternoon, with wind gusts at 20-22 kts. These conditions should improve later this evening into tonight. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 43 62 42 62 / 80 10 0 0 ALW 48 66 45 65 / 80 30 10 0 PSC 48 69 46 69 / 50 10 0 0 YKM 41 65 40 66 / 30 10 0 0 HRI 45 68 45 67 / 60 10 0 0 ELN 41 64 40 62 / 50 20 10 0 RDM 38 55 34 58 / 20 20 0 0 LGD 41 59 39 58 / 90 30 10 0 GCD 40 58 37 59 / 90 50 20 0 DLS 48 63 46 61 / 60 10 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...90 LONG TERM....83 AVIATION...97