Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/18/21

Area Forecast Discussion
National Weather Service Burlington VT
1018 PM EDT Wed Mar 17 2021 .SYNOPSIS... A mild night is on tap ahead of a cold front, with scattered rain showers and mountain snow showers. Thursday will see morning showers press southward with cloudy skies and cooler air in the wake of the front, while an area of light rain moves over southern Vermont which may end as a brief period of snow late in the day. Blustery conditions overnight into Friday will be followed by a steady warming trend with day after day of sunshine and low humidity yielding large diurnal ranges. && .NEAR TERM /THROUGH THURSDAY NIGHT/... As of 1012 PM EDT Wednesday...Did update pops again to place values near 100% for southern Windsor/Rutland Counties on Thurs. In addition, did increase pops along the International border area into the likely range aft 06z tonight. A very light band of precip is crntly developing on radar with a few obs showing precip reaching the ground upstream over the Great Lakes/Southern Canada. Llvl moisture advection will continue with cloud deck lowering and bl rh values increasing overnight on southerly winds. Any qpf acrs northern NY into mtns of VT will be light and generally under 0.10. Continued with schc/chc pops for the CPV, as moisture with southwest flow ahead of boundary will limit potential for measurable precip. Slightly better window as winds shift to the northwest behind boundary with some localized upslope lift. Otherwise, latest 00z NAM and HRRR continue to show a 3 to 4 hour window for light rain, changing to mtn snow across Rutland/Windsor Counties on Thurs. QPF generally 0.10 to 0.20 with an inch or two of snow possible above 3000 feet south of Route 4. Temps hold mainly in the mid 30s to lower 40s tonight, but drop aft 18z on Thurs, with developing llvl caa behind boundary. All covered well in fcst. Previous discussion below: Still looking at light amounts of precipitation to impact most of our area tonight, and southernmost areas tomorrow afternoon. Latest trends have backed off on snowfall chances for south central Vermont as dry air associated with a northern stream trough overpowers the moisture associated with a southern stream low pressure system. The light rain and high terrain snow during this period will be the only precipitation for the next several days. See below for details. It will be a mild night as moist southwest flow moves through the North Country ahead of a cold front. Temperatures will not fall below 40 across the warmest locales of the Saint Lawrence and Champlain Valleys, and even elsewhere we should see temperatures stay above freezing apart from the highest terrain above 2500 feet and the coolest hollows in the Adirondacks and Northeast Kingdom. So expect all rain tonight as fairly wide coverage of showers develops tonight after 10 PM and spreads eastward initially across the far northern tier before spreading quickly southward towards daybreak in along a surface cold front. HREF indicates strengthening 700 and 850 millibar westerly flow tonight associated with a mid-level trough that the initial batch of showers will be tied to. So we should see significant shadowing effect of the terrain during the overnight hours, with showers become briefly moderate across the western slopes of the northern Vermont Piedmont and Green Mountains through the overnight hours. As winds aloft weaken towards daybreak, should see more showers across lower elevations with a couple hours of wet weather ahead of the frontal passage. By afternoon, with a plethora of dry air in the low-levels and rising motions behind the front, chances of precipitation will be just about zero for most of the area. Deeper moisture will hold on in southern portions of Rutland and Windsor counties, where we continue to expect light rain to fall during the afternoon. The main change with this forecast is a faster push south and east of precipitation tomorrow night. This means by the time temperatures fall to near freezing at the lower elevations, precipitation will likely be over. It also results in a small reduction of precipitation amounts to mainly 0.1" to 0.2" in this area. The rest of our forecast area should generally see up to 0.1" of liquid through the next 24 hours, apart from the western slopes of the Greens where locally higher amounts are forecast. The cold air advection moving southward into the area tomorrow will keep temperatures from rising much, with highs ranging through the 40s with values steadying and then falling in the afternoon hours, especially over northern areas. While the combination of breezy conditions and colder air will make for blustery conditions in the overnight hours, the source air does not appear to be nearly as cold as what we dealt with a few days ago. Wind chills will fall into the single digits or lower by daybreak. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 328 PM EDT Wednesday...Friday will be the coldest day for the foreseeable future with temperatures expected to remain below freezing at most locations following the cold front on Thursday. A very slight chance of light snow will be possible across far southeastern Vermont early Friday morning but dry air will bring a plethora of sunshine to the region during the afternoon hours. Lows Friday morning and again Friday night will be in the upper single digits to mid teens. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 328 PM EDT Wednesday...A 1038 mb surface high will begin building across the region on Saturday and will remain overhead through at least Monday before it ever so slowly begins to shift eastward. We will see our 850 mb and 925 mb temperatures climb through the weekend as we enter a more favorable advection regime which will allow temperatures to climb into the 40s on Saturday and into the 50s for Sunday. Given low temperatures a good bit below freezing and highs well above freezing, this weekend is shaping up to be very favorable for those who are tapping maple trees. This trend of above normal temperatures will continue through at least the middle of the week with long term guidance hinting at this period of above normal temperatures continuing well into next weekend. With high pressure firmly entrenched across the region through much of the forecast period, sunny skies and dry conditions will prevail. Fire concerns begin to grow next week as we are quickly digging ourselves into a rainfall deficit with sunlight baking our 10 and 100 hour fuels across the Champlain and St. Lawrence Valleys. The next chance of rainfall won`t come until Wednesday but even then we are looking at just a slight chance at best. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Through 00Z Friday...VFR crntly at all our taf sites will become mvfr cigs at slk/btv/mpv and rut aft midnight with a window of ifr vis/cigs possible at rut/mpv and slk toward 12z on Thurs. Scattered rain showers are possible after 06z, especially mtn taf sites ahead of a sfc cold front with south winds 5 to 10 knots. These winds shift to the northwest btwn 14z-18z on Thurs, as precip is mainly trrn focused at best, before dissipating and cigs increasing by Thurs evening acrs our taf sites. Rutland has the best potential for a period of light rain on Thurs with low cigs and vis in the 3-5sm range. Outlook... Thursday Night: VFR. Slight chance SN. Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Kutikoff NEAR TERM...Kutikoff/Taber SHORT TERM...Clay LONG TERM...Clay AVIATION...Taber
Area Forecast Discussion
National Weather Service Billings MT
556 PM MDT Wed Mar 17 2021 .UPDATE... Building high pressure aloft will bring dry/clear weather to our region tonight. As low level winds veer to the southeast, boundary layer moisture will increase in our far east, courtesy of snow melt in WY/SD today. HRRR is starting to suggest fog in Fallon and Carter counties so have updated for patchy fog from 09-15z. JKL && .DISCUSSION... Tonight through Friday night... A strong 500 MB Ridge will build over the region the next couple of days producing a dry warming trend. Highs will warm into the 50s and 60s Thursday, with mostly 60s to near 70 degrees on Friday as we get an additional boost from pre frontal warming. Look for some gusty wind 25-40 mph developing in the Livingston/Nye foothills picking up by tomorrow and increasing some late Friday with a few gusts over 50 mph possible. The ridge breaks down Friday night as an upper trough moves into the Rockies and high plains. This will spread some precipitation in from the west Friday night into Saturday. Some snow is expected in the high country, but lower elevations will likely remain rain showers. BT Saturday through Wednesday... Somewhat active period in store for the extended with highs in the 40s and 50s each day. Model clusters showed a Pacific trough moving toward the region on Saturday. Precipitation amounts were around a tenth of an inch /0.10/, with a quarter inch /0.25/ in the Beartooths/Absarokas. The ECMWF EFI was rather unstable in the western zones, which could indicate some thunder. Checked the GFS sounding for KLVM and CAPE was low but there were decent lapse rates. Still, not strong enough support to put in thunder at this time, but it is something to watch. Rain was likely over the central and W, with several inches of snow likely in the mountains. Chances for rain and snow continue into Sat. evening. The trough will still be in the region on Sunday, but best chances for precipitation will be S of the area. Next trough moves into the Pacific NW on Monday, but the clusters were not in great agreement with the system. NBM brings chances for rain and snow into the SW half of the area Mon. night and Tuesday. For Wednesday, most cluster members have a ridge building in, but Cluster 4 is showing a Pacific NW trough. NBM keeps the area dry. ECMWF Ensemble wind gusts showed gusts in the 20s and 30s for much of the period. NBM did have gusty winds over portions of the area during the period. Overall, there were no high impacts during the extended. Arthur && .AVIATION... Building high pressure aloft will bring widespread VFR through Thursday. There could be localized valley fog near KBHK-K97M between 09-15z (IFR or lower possible). SW wind gusts of 20-30 knots expected at KLVM tomorrow. JKL && .PRELIMINARY POINT TEMP/POPS... Thu Fri Sat Sun Mon Tue Wed ----------------------------------------------------------- BIL 029/062 037/068 040/051 034/052 030/054 033/049 030/055 00/U 00/U 47/R 31/B 11/B 23/O 10/U LVM 029/061 037/061 036/048 029/047 025/047 028/044 026/050 00/U 01/N 47/O 31/B 12/O 33/S 11/U HDN 024/062 030/069 037/053 032/054 028/056 032/051 029/055 00/U 00/U 27/R 32/O 11/B 23/O 11/B MLS 021/057 030/066 037/053 033/054 029/055 031/051 029/053 00/U 00/U 04/R 21/B 01/U 11/E 00/U 4BQ 022/056 030/066 037/056 033/052 029/054 031/049 029/052 00/U 00/U 04/R 21/B 11/B 12/O 11/U BHK 020/052 027/063 034/055 031/052 027/053 028/048 026/050 00/U 00/U 03/R 21/B 11/U 11/E 10/U SHR 020/055 028/063 032/052 028/047 024/049 027/044 024/049 00/U 00/U 06/R 43/O 12/R 24/S 21/B && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$
National Weather Service Kansas City/Pleasant Hill MO
1056 PM CDT Wed Mar 17 2021 .Update... Issued at 1004 PM CDT WED MAR 17 2021 With precipitation struggling to develop north of I-70, have canceled the northern edge of the winter weather advisory. Otherwise, forecast remains on track. Update Issued at 833 PM CDT WED MAR 17 2021 Vigorous low pressure system moving towards the southwestern tip of Missouri as of 02Z Thursday. Precipitation shield is filling in south of I-70 with strong dynamics. Have seen a few sporadic reports of light snow across the area, but as drier air filters in from the north, combined with strong dynamics, expect precipitation to switch over to snow despite surface temperatures remaining above freezing overnight. Am concerned with the weakly negative equivalent potential vorticity, which suggest the potential for a scattered lightning strike or two throughout the overnight hours. Could also see some enhanced pockets of snowfall with the potential convective elements. Followed day shift lead, and have been closely following short term Hi-res models for the evening update. Have massaged snow amounts upwards slightly for the southern metro and and areas just east along the Missouri River. Have also expanded the winter weather advisory to include Saline and Carroll counties. Update posted. && .Discussion... Issued at 227 PM CDT WED MAR 17 2021 Key messages: - Accumulating snow is likely tonight. A few inches of a heavy wet snow across eastern Kansas and western Missouri are expected. - Quieter and warmer weather this weekend. Detailed discussion... An intense upper-level storm system is tracking across Oklahoma this afternoon. This system will track to our south this evening and overnight. Models are in decent agreement with the overall strength and track of the system. The main differences come in just how cold temperatures might get tonight and how that would affect potential snow amounts. When looking through items that would support heavy snow, this system checks a lot of the boxes. There is very strong and very deep upward vertical motions that will move over the area tonight. There is a well defined TROWAL with the deformation area coincident with the strong upward vertical motions. The moisture transport into the TROWAL/deformation area is very strong. Cross sections running roughly west-to-east across the area show theta lines folding over aloft over the area, indicative of an unstable environment. This is supported by a large and deep area of slightly negative equivalent potential vorticity (-EPV), all coincident with the deformation area of precipitation. The jet structure is impressive with strong diffluence aloft noted. All this indicates that there will be intense upward vertical motion. Despite all these very favorable features of this system, temperatures in the lowest part of the atmosphere will likely remain above freezing with temperatures at the surface dipping into the low to mid 30s. Given the intensity of the upper-level support with this system, have made some changes to our forecast T and Td grids to allow snowfall to accumulate. Have trended toward colder solutions like the HRRR and NAM for surface T and Td. This lowers temperatures into the mid 30s and dewpoints into the lower 30s during the heaviest precipitation. The intense upward vertical motions should dynamically cool the atmosphere and allow temperatures to be cooler within the heaviest areas of precipitation. With this cooler trend, snow accumulations look likely from eastern Kansas through west central Missouri. For now, it looks like anywhere from 1-3 inches will be possible in this area, with some isolated amounts around 4 inches. These amounts will be most likely on grassy surfaces with lower amounts on the relatively warmer paved/cement roads. With temperatures only dipping into the mid 30s, it will take higher snowfall rates to overcome the relatively warmer pavement temperatures, cutting into accumulations. But with all that said, will run with a winter weather advisory from midnight tonight to noon tomorrow for parts of eastern Kansas and western Missouri. There may be places outside of the advisory area that still see snow, but those amounts currently look less than an inch. With the same pavement caveats previously mentioned there may be minimal impact to travel with the overall lower amounts. Quieter weather will prevail after this system moves out of the region. Temperatures will rebound into Saturday and especially Sunday with highs climbing into the climbing into the upper 50s to 60s Saturday and middle 60s on Sunday. The next chance for precipitation will come Sunday night into Monday as another upper- level shortwave trough tracks across the middle of the country. && .Aviation...(For the 06Z TAFS through 06Z Thursday Night) Issued at 1051 PM CDT WED MAR 17 2021 Upper low across south central Missouri as of 04Z will continue to pinwheel east into Thursday. Precipitation in the form of rain and snow is expected to mainly remain along and south of I-70 across western Missouri. Have therefore trimmed back precipitation at KSTJ, KMKC and KMCI; however, IFR ceilings along with strong gusty north winds will remain. Expect ceilings to gradually improve throughout the day Thursday as precipitation comes to an end as upper low works east. Gusty winds are not expected to subside until Thursday evening. && .EAX WATCHES/WARNINGS/ADVISORIES... KS...Winter Weather Advisory until noon CDT Thursday for KSZ057-060- 104-105. MO...Winter Weather Advisory until noon CDT Thursday for MOZ029>031- 037>039-043-044-053. && $$ Update...BT Discussion...CDB Aviation...BT
Area Forecast Discussion
National Weather Service Green Bay WI
1033 PM CDT Wed Mar 17 2021 Updated aviation portion for 06Z TAF issuance .UPDATE... Issued at 715 PM CDT Wed Mar 17 2021 Strong NE winds are anticipated Thursday as the forecast area becomes situated between a building anticyclone over Ontario and a cyclone tracking up the Ohio Valley. The tightest pressure gradient will remain across southern Wisconsin. But east-central Wisconsin and in particular the Green Bay area is susceptible to strong NE flow funneling down the Bay. Mixing on model forecast soundings suggests gusts into the low 30s (kts) at GRB. But most of the soundings also showed considerably stronger winds (up to 46 kts on the HRRR) at 2K ft. In addition, the soundings indicate almost no directional shear between the surface and 10K ft. That may allow for somewhat strong winds than would normally occur given the forecast low-level thermal profile. Bumped sustained winds and gusts in the GRB area up, and will expand the WI.Y into Brown county. Additional expansion into the rest of E-C WI may be needed later, but there is still enough uncertainty to hold off on doing that now. A major concern with the wind is what will happen to the ice floating around on the Bay of Green Bay. Glimpses of the bay surface seen on afternoon VIS satellite imagery through breaks in the clouds showed almost all the ice consists of loose chunks that were drifting north in the light south flow. That ice will be driven back to the SW by the strong NE winds tomorrow. It`s extremely difficult to determine exactly when and where there will be substantial ice shoves as there are numerous factors that come into play. But at least the wind seems very favorable. So will issue a LS.Y for Brown county to match the WI.Y. Ice shoves could also occur in Oconto, Marinette, Door and Kewaunee counties as well, but the risk isn`t as great as in Brown county so will leave those areas out of the advisory, at least for now. The ice shoves and erosion due to wave action could result in some damage at the shoreline. But the potential for flooding is not as great as it would have been last year because the water level of the bay/lake is lower. Updated product suite will be out ASAP. && .SHORT TERM...Tonight and Thursday Issued at 341 PM CDT Wed Mar 17 2021 A mix of snow, rain, and graupel continue across east-central Wisconsin this afternoon as a mid level shortwave tracks through the western Great Lakes region. The HRRR model captured this flare up of precipitation fairly well in the last few runs, keeping precipitation in across the area through the afternoon then diminishing by early evening as the main shortwave shifts off to the east. As temperatures continue to rise, the threat for accumulating snow should be fairly minimal. However some bursts could cause a few tenths of an inch to pile up in some locations. Clearing skies are then expected tonight as the main shortwave tracks east and high pressure builds in across the northern Plains. Lows tonight are expected to fall into the middle to upper 20s across the north, with lows around 30 across east-central Wisconsin. The area will be in between a low passing through the Ohio Valley and the aforementioned high building in across the northern Plains. This will mean a very tight pressure gradient will exist across the forecast area on Thursday, causing gusty northeast winds of 35 to 45 mph at times. The worst conditions will be across the lakeshore counties with unabated flow off Lake Michigan. These areas will have the best chance of hitting headline criteria on Thursday. Further inland the Fox Valley looks to be just below criteria at this time; however, funneling through the bay of Green Bay may necessitate a headline in subsequent forecasts. At this time will issue a Wind Advisory for the lakeshore counties given the higher certainty and hold off for the Fox Valley. The gusty northeast winds could push ice into the southern bay and possibly cause minor flooding. Highs on Thursday are expected to hover around 40 along the lakeshore, with the highest values farther inland across central Wisconsin with highs in the upper 40s. .LONG TERM...Thursday Night Through Wednesday Issued at 341 PM CDT Wed Mar 17 2021 Quiet early spring conditions are expected Thursday night into most of Sunday. Then an unsettled pattern is setting up for next week with at least three systems to impact the area. Each will bring rain, some wind and possibly some wintry precip. Temps look to be above or well above normal. Thursday night...low pressure will work into the Mid-Atlantic as high pressure builds into the Great Lakes. This will allow winds to diminish through the evening hours. Lingering lakeshore flooding and ice shove issues could persist (if already occurring) through around midnight. Could be some lingering clouds in the southeast early, then look for clear skies. Winds look to be the lightest over the north, where temps will drop to 10-15 degrees in the cold spots. Some single digits would be possible where some snow remains on the ground. The rest of the area will be in the teens to lower 20s. Friday into the weekend...high pressure settles over the Great Lakes on Friday bringing quiet weather conditions. Look for light winds and plenty of sunshine. The clear/sunny skies continue into Saturday as the high pressure slides east of the region and weak return flow sets up. Clouds start to increase Saturday night into Sunday as stronger WAA moves into the area, a frontal boundary works towards the area and the dry air gets pushed eastward. Temps will get a boost Saturday into Sunday as 925/850mb temps slowly increase within the WAA pattern. If spots don`t make a run at 60 on Saturday, many should on Sunday. Exception will be near Lake Michigan where the south winds will keep temps in the 40s to around 50. South winds will pick up slightly on Saturday, mainly 10-25 mph, then a breezy day expected on Sunday with south winds gusting up to around 30 mph. Relative humidities will be low Friday and Saturday afternoon, which could lead to some fire weather concerns, especially as winds pick up. Sunday night into next the frontal boundary and upper trough swing into the area, chances for showers returns to the area, but overall coverage looks to be low. Chance for rain showers continues on Monday as the frontal boundary stalls in the area and washes out as low pressure develops over the Plains. Temps will be a little cooler near/behind the front, but another spring-like day is expected south of the front with 50s to low 60s expected, cooler near Lake Michigan. Closed low pressure will move from the Plains Tuesday and into the western Great Lakes on Wednesday. This will spread a large area of showers into the area Monday night into Tuesday. Could see some thunder make it into the area eventually, as lapse rates steepen and a shortwave tracks into the Great Lakes, but this might be closer to Tuesday night and Wednesday. Likely will get a pretty good slug of moisture ahead of this system, with some locally heavy rain a possibility. Depending on the track, some snow will be possible on the back side of the mid-week system, but way too early to dive into those details. && .AVIATION...for 06Z TAF Issuance Issued at 1032 PM CDT Wed Mar 17 2021 The chance of getting MVFR conditions has diminished, though there could still be some patches of clouds flowing into the area off Lakes Michigan or Superior at times. But the main aviation concern will be strong/gusty NE winds Thursday which will impact takeoffs and landings. Some LLWS is likely late tonight to mid- morning Thursday as winds aloft increase more quickly than surface winds. && .GRB WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 7 AM to 7 PM CDT Thursday for WIZ022-039-040- 050. Lakeshore Flood Advisory from 7 AM to 7 PM CDT Thursday for WIZ039. && $$ UPDATE.........Skowronski SHORT TERM.....Kurimski LONG TERM......Bersch AVIATION.......Skowronski
Area Forecast Discussion
National Weather Service Indianapolis IN
1153 PM EDT Wed Mar 17 2021 ...Updated Aviation Discussion... .Forecast Update... Issued at 942 PM EDT Wed Mar 17 2021 Surface analysis this evening shows deep low pressure in place across southern MO....with a warm frontal boundary stretching northeast across IL to Northern Indiana. Light southeast flow was in place across Central Indiana. Dew points were in the moist upper 40s to lower 50s. GOES16 shows abundant cloud cover across the area. Water vapor imagery shows a deep upper low over OK with tropical moisture streaming north through the Tennessee and Ohio Valleys. The surface low is projected to continue on its path northeast along the warm front overnight...approaching Central Indiana. Late this evening radar returns have diminished across Central Indiana as weak ridging remains in place aloft. More organized precipitation looks to be found across Western KY...ahead of the approaching low. HRRR keeps rather minimal echos across Central Indiana the next few hours...however rain looks to become more widespread late tonight as the low approaches and rain along with the associated forcing arrive late tonight. By 12Z forecast soundings and time heights reveal a saturated column. Thus have trended pops lower for the next few hours as measurable precip seems unlikely...but ramped pops back up late overnight as better forcing arrives. Given the expected rain and minimal cooling along with moist dew points also trended overnight low warmer by 1-2 degrees. && .Short Term...Tonight through Thursday Night Issued at 338 PM EDT Wed Mar 17 2021 A strong and stacked low-pressure center will track west-to-east from the Ozarks tonight, and then up the Ohio Valley Thursday... bringing the greatest rainfall since late November to much of the region tonight-Thursday morning. Chances for rain showers will increase from southwest to northeast late today and this evening, with widespread definite POPs for the CWA from late this evening through Thursday afternoon. Medium confidence exists in isolated to scattered embedded thunderstorms, especially south of I-70. Any strong/severe thunderstorms would likely be limited to southeast of a Bedford-to-Rushville line...and be isolated at best, Thursday morning-midday. The threat of severe storms Thursday will be focused south/east of Cincinnati...whereas more stable air will have already entered our region before daytime heating will have much chance to destabilize the atmosphere. Storm total rainfall will be 1.00-2.00" across the region. Moderate confidence exists that the axis of maximum rainfall will be parallel to and north of I-70, where totals of 1.50-2.00" are likely, with local totals exceeding 2.00". Nuisance flooding is likely across the region...especially near creeks/streams, in low-lying spots and poor drainage areas. Renewed minor river flooding on central Indiana`s main stem rivers will resume as early as Thursday evening. High temperatures Thursday will range from the mid-40s to near 60F ...while overnight lows will be 45-55F tonight, and then the upper 20s to near 30F for most locations Thursday night as a ridge of Canadian high pressure infiltrates Indiana from north to south. The normal max/min for the short term period is 53/34. && .Long Term...(Thursday night through Tuesday) Issued at 306 AM EDT Wed Mar 17 2021 The long term period looks to begin with the last of the precipitation from the midweek system associated with the SW/NE oriented deformation zone on the northwest side of the low making its way through central Indiana Thursday evening. Expect that precipitation will end by the overnight hours as the low continues to depart and the column dries out rapidly from aloft. High pressure at the surface and aloft will then provide dry weather and warming temperatures through the weekend and into early next week, with generally clear to mostly clear skies and pleasantly mild conditions, especially late in the weekend and early next week as widespread highs in the 60s return. Another in what seems to be a train of closed lows then develops and moves through the region late in the period, bringing another chance for showers to the area. This system looks a bit more progressive at this time, but may prolong or exacerbate any high water produced by the upcoming system, depending on its precipitation output and the eventual speed of travel. && .Aviation...(00Z TAF Issuance) Issued at 1152 PM EDT Wed Mar 17 2021 IMPACTS: - IFR to LIFR conditions are expected to arrive overnight. - IFR to LIFR will continue through much of Thursday. - Gusty easterly winds will develop predawn Thursday and continue through through Thursday. DISCUSSION: Radar trends shows echos over southern Illinois approaching Central Indiana yet still diminishing slightly upon approach. Thus have trended toward VCSH at IND and LAF for the first few hours of the TAF period. These showers should arrive at BMG and HUF near 06Z...thus have used a prevailing rain at those spots. Extensive cloud cover across the area as seen on GOES16 is expected to remain as the deepening low over southern MO continues to push east toward Central Indiana along the warm front in place across Central Indiana. IFR Cigs...particularly on the north side of the low will begin to impact Central Indiana tonight and continue through much of the day on Thursday. Time heights and forecast soundings show saturation within the lower levels through the day on Thursday before some dry air is expected to arrive after 00Z Friday. As the deep low arrives along with the frontal boundary in place...gusty winds are expected to develop late tonight and continue through the day on Thursday. Look for NE winds on Thursday with gusts to 30-40 knots in the morning through the afternoon. Confidence is high in both IFR arriving late tonight along with gusty winds. Low confidence in embedded thunderstorms. && .IND WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 8 AM to 8 PM EDT Thursday for INZ021-028>031- 037>042-048-049-057. && $$ Update...Puma Short Term...AGM Long Term...Nield Aviation...JP
National Weather Service Jackson KY
1131 PM EDT Wed Mar 17 2021 .UPDATE... Issued at 1131 PM EDT WED MAR 17 2021 Made only minor revisions to blend late evening obs into the forecast, with no substantive changes overall. UPDATE Issued at 1049 PM EDT WED MAR 17 2021 Have updated largely for timing of rounds of precip and thunder potential over the first couple of periods. The 18Z GFS and most recent HRRR were in reasonably good agreement and were verifying well for precip this evening, and were used to refine the forecast. && .SHORT TERM...(This evening through Thursday night) Issued at 305 PM EDT WED MAR 17 2021 18z sfc analysis shows a deepening area of low pressure to the southwest of Kentucky with a warm front pushing a band of showers and possible thunderstorms into downstream portions of the Cumberland Valley. The thickening clouds, and a foggy start in many places, have kept temperatures from making it quite to the low 70s for most with even some upper 50s in the southwest as the pcpn is moving overhead. Dewpoints are up from yesterday, though, with upper 40s found north and low to mid 50s south while winds are running southeast at 5 to 10 mph - for the most part. The models lose some agreement tonight before actually come into better alignment aloft on Thursday. They all depict ridging pushing out of the area to the east later tonight in the face of a deep closed off 5h low rolling into the western Tennessee Valley. The GFS and Canadian initially take this meteorological bowling ball east quicker than the ECMWF and NAM. However, they come back in line with each other on Thursday taking the core of the trough through southern Kentucky. As such, confidence is rather high during this critical part of the forecast that the blended NBM is a good starting point to the grids. Later Thursday night the NAM starts to deviate more with its low dropping more south than east. Will take that solution into consideration through Friday morning during an upslope situation that the NWP models always struggle with. Sensible weather will feature a pretty active period of weather from this evening into Friday morning. Showers will quickly work northeast through the CWA this evening as the lead surge of moisture outruns the warm front - leading to a diminishing trend to those first showers. Another surge of moisture them reloads along the warm front and more effectively moves into the area late this evening and overnight with plenty of lift found over the JKL CWA, at times. Some heavy rain and training of showers and storms can be expected later tonight - will add mention of this to the HWO. The core of this will shift east during Thursday morning with the warm front - placing eastern Kentucky in warm sector for the rest of the day. This is a particular concern as dry slotting will make for a window of opportunity for destabilization and the ability to tap into the high amount of directional shear aloft. This shear is maximized as the core of the sfc low passes overhead in the afternoon. For this reason a good portion of our area is in a slight risk for severe weather on Thursday afternoon with the rest in a marginal risk. Organized storms will be a strong threat with a potential for damaging wind gusts the main concern, but the tornado chances, while low, will not be zero. The sfc low moves east Thursday evening with its backside and wrap around pcpn moving into this part of the state in its wake that night. CAA on brisk west to northwest winds into Friday morning will drop temperatures into upper 30s by dawn for most with even a touch of non-accumulating snow and some mid 30s occurring over the Bluegrass region and north of I-64 by dawn. We will keep watching this snow threat in further model runs. Given the high moisture - did not deviate much from the NBM values for the T grids through the forecast. For the PoPs - mainly brought them up through most forecast periods with some dry slot timing refined from the NAM12. .LONG TERM...(Friday through Wednesday) Issued at 323 PM EDT WED MAR 17 2021 A few rain showers will be exiting the area on Friday, as a large and powerful area of low pressure moves off to our east. The rain should be out of eastern Kentucky by late Friday morning. We will see well below normal temperatures around eastern Kentucky on Friday, as cooler air spills into the area behind the departed area of low pressure. However, the air mass should modify fairly quickly on Saturday, with mostly clear skies and ample sunshine expected. Highs on Saturday should max out in the mid to upper 50s, which is right about normal for this time of year. After that, as a ridge of high pressure becomes firmly established over the region, we should several days in a row with above normal temperatures and dry weather. A few rain showers may move back into the area Tuesday evening and night, but this a very uncertain scenario at this time. Highs should be in the 60s each day from Sunday onward, with a gradual warming trend occurring during that time. By the time Wednesday rolls around, daytime maxes should be in the upper 60s to lower 70s around the area. Nighttime lows will start out in the upper 20s to lower 30s over the weekend, but should become quite mild into mid-week, with nightly values only falling into the 30s and 40s from Sunday night through Tuesday night. Strong and gusty winds will be possible for Friday, as the pressure gradient on the back edge of the departing low intensifies. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) ISSUED AT 1049 PM EDT WED MAR 17 2021 Conditions were mainly VFR to start the period, but there were some sub-VFR conditions near the TN border in association with precip moving northeast into the forecast area. This precip as since made its way further northeast and diminished greatly. However, additional precip over TN and western KY should also move through during the night and early Thursday. Along with this, MVFR and IFR conditions are forecast to develop overnight. As the bulk of the precip departs to the east on Thursday morning, VFR conditions should return. However, more showers are possible after some heating, especially in the afternoon. We could also see some thunderstorms, with the best chance in most locations being on Thursday afternoon. Any of the showers or thunderstorms on Thursday could bring localized sub-VFR conditions. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...HAL SHORT TERM...GREIF LONG TERM...AR AVIATION...HAL
Area Forecast Discussion
National Weather Service Louisville KY
1029 PM EDT Wed Mar 17 2021 .Forecast Update... Updated 1025 PM EDT Wed Mar 17 2021 We`ve had a break from the precip for most of the CWA over the past few hours, but regional reflectivity shows another precip shield over western KY and TN. Radar returns are already beginning to intrude our south-central KY counties. 00z sfc analysis shows our region split between two frontal features, with the sfc low located over southern MO. Tonight, we will see another round of showers as the sfc low continues eastward and rides up the Ohio River as a stationary front extends to the east and sits along southern IN. Believe the reflectivity we are seeing in TN will lift NNE and into KY over the next few hours. SPC mesoanalysis is not showing any sfc based instability to speak of, but PWATs are around 1.2". Our severe weather potential continues to diminish for the overnight hours, but can`t completely rule out a possible flooding threat. Low 6-hr FFG over our SE CWA (Clinton, Cumberland, Monroe) is where our highest QPF for tonight if forecast. While current 6-hr QPF does not exceed the FFG, any heavier cells or training precipitation could lead to some flooding concerns. By 08z, hi-res CAMS are wanting to bring more of a cellular precip from SW to NNE through the CWA. However, CAMS initialize these cells over NE AR by 02z, but current radar trends are not matching up too well with this. Will need to continue to monitor the initialization of those cells, as those could be our best chance of possibly seeing a stronger storm. Confidence remains low in seeing convection tonight. HRRR continues to paint a region of 500-750 J/kg of SBCAPE after 09z tomorrow morning, but it appears the CAPE will be constantly trying to catch up to the better moisture. With the bulk of the moisture and better lift staying ahead/north of the instability, think we will be limited to just some rain showers instead of any convection for the overnight and into tomorrow morning. && .Short Term...(This evening through Thursday) Issued at 320 PM EDT Wed Mar 17 2021 A surface low, currently near the Ozarks, will continue to slowly move to the east under a mid-level closed low, and by tomorrow evening, the slow moving system will only make it as far as Kentucky. This slow movement will provide ample time for central Kentucky and southern Indiana to receive plenty of precipitation with the majority of that coming tonight. Tonight, precipitable water values range from 1.2 to 1.5 inches, and the CWA is expected to remain relatively stable. This will result in more rain showers and less thunder. The best chance for thunder will likely be from near sunset through around midnight. Areas in the southern half of central Kentucky could see a line develop around 21- 22z and work it`s way east. Believe this is probably going to be the best chance at any severe weather as strong directional and speed wind shear exists, but again instability is weak and LCL heights are high. Low level lapse rates are weak too. This will limit the high wind threat. Expectations of severe weather are low, but always have to watch high shear values. Expect mild low temperatures as they only drop to into the upper 50s. Tomorrow, a dry slot is expected to work it`s way through the CWA choking any remaining precipitation. Precipitable water values drop below an inch, so when precipitation builds back across the area by late afternoon, expect only light rain shower. Highs are expected to reach into the 60s. .Long Term...(Thursday night through Wednesday) Issued at 252 PM EDT Wed Mar 17 2021 By Thursday evening, the upper low will be over the central KY/TN border as it eventually fills and moves east over the Appalachians. Rain showers will be ongoing Thursday night and exit to our east by Friday morning sunrise. A few snow flakes could potentially mix in behind the departing system early Friday morning in the Bluegrass as cold air filters in from the NW. Gusty NNE winds in the 20-30mph range will also result from a tightening pressure gradient as Canadian high pressure builds in from the north. Expect dry conditions to follow for the weekend and into the early part of next week as the aforementioned high pressure dominates a large portion of the eastern US. Saturday morning will see the coldest temperatures of the period with morning lows in the upper 20s to low 30s. But as the high pushes east, winds will slowly veer to SE accompanied by WAA resulting in gradual warming that will push afternoon temperatures above climatological norms from Sunday through mid week. Highs Sunday will peak in the low to mid 60s, and by Wednesday afternoon highs will reach into the upper 60s. Our next rain chances will return Tuesday through Wednesday ahead of a cold front the looks to push through Wednesday. Will go with model blend solution with chance of rain showers through this period. && .Aviation...(00Z TAF Issuance) Issued at 735 PM EDT Wed Mar 17 2021 Complex and low-confidence forecast in this TAF issuance. Currently catching a break in the precip at SDF/BWG/HNB, and even breaking out into mid-level ceilings. LEX should also break out shortly. The dry and VFR conditions won`t last long as the next batch of showers lifts NE out of western Tennessee. Should deteriorate into a rainy night with prevailing MVFR cig/vis. However, conditions will fluctuate a bit more as we could see ceilings break out to VFR at times, while the heavier showers could result in brief IFR conditions. Tried to handle it in TEMPO groups overnight. Look for another break in precip during morning hours, with a period of VFR in SDF and LEX toward midday. However, forecast confidence really drops here as the mature cyclone makes its way across the Ohio Valley. Dry slot will bring gusty SW winds, but we`ll still need to mention at least VCSH. Precip coverage increases enough late in the afternoon under the cold pool that we`ll go prevailing -SHRA and use TEMPO to reflect potential for vis restrictions. Very low confidence in afternoon wind direction for HNB and SDF as the sfc low passes nearly overhead. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...CJP Short Term...KDW Long Term...CG Aviation...RAS
National Weather Service Morristown TN
912 PM EDT Wed Mar 17 2021 .UPDATE... EVENING UPDATE. && .DISCUSSION... Currently still have showers and the occasional rumble of thunder moving northeast through the eastern Tennesee Valley this evening. We are still looking to our southwest focusing on the location of the warm front as this remains the best chance for storms to begin to tap into the lower level of the atmosphere and realize the strong low level shear. Over the past several hours the front has really slowed its northern progress (like many of the CAMs have been anticipating) and still expect the progress to be slow going over the next several hours. If we can get the front to begin to occlude this will really diminish the severe thunderstorm chances in our forecast area, and some of the hourly CAMs are hinting this may be the final outcome as that front just barely nudges into southeast Tennessee. Will obviously be keeping a laser focused eye on storms moving out of AL/GA, but it may be several more hours for stronger storms to really make significant progress into SE Tennessee. The highest threat for strong to severe storms and tornadoes will continue to be the highest across central/northern Mississippi and Alabama this evening. The more immediate (and likely more impactful) threat will Flash Flooding across SE Tennessee as several rounds of showers and some thunderstorms have moved over the same areas in the southern valley. Radar estimated QPE and ground observations indicate southeast tennessee has picked up widespread 1-2 inches over the past 3-6 hours, with pockets of heavier amounts. Updated Flash Flood Guidance indicates that across the southern row of SE Tennessee counties only need to see about 1" of additional rain over 3 hours to cause Flash Flooding, which is very likely to happen tonight. Reports from law enforcement and EM`s in the areas are already reporting some minor flooding of roads and other low lying areas. With more storms brining even heavier downpours to this area the rest of the night it looks like road closures and flash flooding is likely tonight. A good time to remember that night time flooding is one of the most dangerous weather situations you can encounter and it`s NEVER worth driving through a flooded road even if it looks passable. A flash flood watch remains in effect for the southern Tennessee Valley down into northern Alabama and Georgia for the rest of the night into Thursday morning around sunrise. ABM && .AVIATION... 00Z TAF DISCUSSION. Showers across the area with a few embedded rumbles of thunder in SE TN. Coverage of storms will increase and thunderstorm chances will increase as well, especially around 06z at KCHA as a warm front moves northward. Expect the peak time for thunderstorms to be between 03z to 10z, but a few isolated strikes can occur outside these times. Flying conditions will remain poor overnight as strong to severe storms move into the area from AL/MS/GA. Don`t expect improvement in conditions until these storms move out by mid morning. Another round of scattered rain could occur during the day tomorrow, but kept mention out to limit TAF length and focus on the first round of storms tonight. ABM && .PREV DISCUSSION... /ISSUED 337 PM EDT Wed Mar 17 2021/ SHORT TERM...(Tonight through Thursday) Key Messages: 1. Scattered showers/thunderstorms will lift northward this evening with locally heavy downpours possible. 2. A line of strong to severe thunderstorms will reach the S Plateau near Midnight and move across the S Valley and SE TN reaching SW NC by 10 or 11Z. 3. Wind damage, large hail, locally heavy rain, and a low chance of isolated tornadoes are expected across the S Plateau and the S Valley as the line moves through. 4. This line will also affect parts of the N Plateau, N and central Valley, NE TN, and SW VA late tonight as it moves eastward, but only pockets of wind damage and hail are the main threats in those areas. 5. The storm threat for Thursday has greatly diminished. Discussion: Late Afternoon/Evening... A band of convective showers is moving N across the Plateau and S and central Valley as of mid afternoon. Lightning activity has nearly all diminished, but a rumble of thunder and brief moderate rainfall remains possible as this band continues to lift to the N and NE toward NE TN into SW VA. This elevated convection has been tied to WAA and isentropic ascent north of a low/mid level warm front that is now quickly moving N, and a 30-40 kt LLJ across AL has been advecting elevated instability northward. However, much of the East TN Valley has been in cooler, much more stable air, which is why the lightning has diminished. Nevertheless, kept thunder in the forecast grids through the evening as the LLJ strengthens and advects greater amounts of elevated instability into our region. Latest surface analysis shows the surface warm front still well to the S across central AL, where surface based convection, including discrete supercells, have been exploding over the past 1 to 2 hours in a highly sheared environment. It is this surface warm front that will dictate how much severe weather we see across the S Plateau and S Valley overnight (see tonight section below). Tonight... Meteorology and Hazard Overview As the deep, closed mid/upper low currently near the OK/AR borders lifts ENE through the mid MS Valley tonight, the surface low nearly stacked beneath it will deepen to around 995 mb over central IL by Thurs morning. This will pull the aforementioned surface warm front NE into the S Plateau and S Valley after Midnight, and the latest RAP and HREF members project this front to reach the far S Plateau and S Valley (Marion and Hamilton Counties) in the 06-09Z timeframe. It is common for the warm front to surge N a little faster than guidance predicts, and the left exit region of a 110-120 kt upper jet will force a 50+ kt LLJ helping to force the front N, so would not be surprised to see it reach these southern areas by 04Z. Low- level shear and SRH continue to look very high in the vicinity of the surface warm front with 40-50 kts of 0-1 Km shear, 300-600 m2/s2 of 0-1 Km SRH, and 400-700 m2/s2 of 0-3 km SRH. However, the location of the frontal boundary will dictate tornado potential because it will not only locally enhance the shear, but it will mark the surface instability/theta e gradient. The latest RAP and HREF project a few hundred joules of surface based CAPE along and S of this warm front, and with the highly sheared environment, this leads to significant tornado parameter values (STP) of 1 to 1.5 across the S Plateau into the S Valley, especially Marion, Hamilton, S Bledsoe, and perhaps parts of Bradley counties. This area will need to be monitored closely for a few tornadoes possible in the roughly 04 to 09Z timeframe. Farther N, the instability will be elevated, so despite very impressive deep layer and low-level shear up there too, convection will mainly produce large hail with pockets of damaging winds. Convective Evolution/Timing In terms of how the convection will evolve, scattered multi-cell clusters lifting out of AL this evening will give way to a QLCS moving in from the W, and this QLCS should cross in the 04-10Z timeframe. It will likely reach the S Plateau and S Valley W of I-75 between 04 and 07Z, then cross the rest of the region in the 07-10Z timeframe. As stated earlier, a few tornadoes are possible in the S Plateau and S Valley, and these will generally occur with rotation embedded in the QLCS, but we`ll need to watch for discrete cells ahead of the line depending on how quickly the warm front can surge into that area. Flooding Potential and Mountain Winds Another hazard will be locally heavy rainfall leading to localized flash flooding. This will generally be limited since the convection will be moving fast (40+ kts), but the S Plateau, S Valley, into SW NC have the greatest chance to see some flooding since that area saw 1-2 inches of rain yesterday. High Wind Warning remains in effect for the E TN mountains and foothills this evening through 18Z Thurs as the 50+ kt LLJ crosses the terrain. The flow will be SW and not overly perpendicular to the terrain, but the high speeds will lead to warning criteria winds of 70+ mph in the highest peaks. Thursday... The early morning QLCS will exit E quickly after 11 or 12Z, and as the storm system continues to shift toward the lower OH Valley, it will occlude with the cold front crossing our region rapidly behind the warm front. This greatly limits the amount of recovery time that we will have in the narrow warm sector before the cold front crosses in the late morning to early afternoon timeframe. CAMS have caught onto this idea with only a scattered, weak line redeveloping during the mid morning. Deep layer shear remains strong ahead of the cold front (60-80 kts 0-6 Km), but low-level shear and SRH will quickly diminish, and with the limited instability/lack of recovery time, do not expect much in the way of severe weather. Scattered showers/thunderstorms with 40-50 mph winds, small hail, and limited lightning are the most likely scenario quickly moving W to E from mid morning through early afternoon with all activity gone by 17Z. As the upper low and associated cold pocket aloft approaches during the afternoon, WBZ heights lowering below 6000 ft and surface warming will create low-level instability for scattered, low-topped convective showers capable of pea sized hail, so kept chance PoPs through the afternoon and evening. Highs in the 65-70 degree range in the morning will fall through the 60`s during the afternoon. Garuckas LONG TERM...(Thursday Night through Wednesday) Closed H5 low will be entering the Plateau as Thursday night begins. Models are slightly disputing the path of its center, with the NAM the southernmost solution passing south of Gatlinburg, while the GFS, ECMWF, and CMC keep the center north of I 40. That NAM solution generates some mountaintop snows by 12Z Friday, so there may be some accumulations above 5000 feet. Otherwise, the precip ends quickly from the west Friday, lingering longest and lightly over the mountains. Afterwards, high pressure will dominate the area for several days, with dry and warming weather Saturday through Tuesday. The next uncertainty is how long the ridge of high pressure can hold. Troughing takes hold across the western U.S., and the next weather system to approach us will eject out of that broad western trough. The GFS is quickest with the onset of rain, impacting us late Tues through Wed. But the ECMWF and CMC are stronger with our ridging and keep us dry through next Wednesday night. So I`m just tossing in low POPs for next Tues night through Wednesday night until we and surrounding offices can lean more firmly one way or the other. GC && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 59 64 46 56 39 / 90 40 20 10 10 Knoxville McGhee Tyson Airport, TN 60 69 45 53 35 / 90 80 60 20 10 Oak Ridge, TN 59 66 44 54 35 / 90 80 60 10 10 Tri Cities Airport, TN 55 70 42 52 30 / 80 90 80 30 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...Flash Flood Watch until 8 AM EDT /7 AM CDT/ Thursday for Bledsoe- Bradley-East Polk-Hamilton-Marion-McMinn-Meigs-Rhea- Sequatchie-West Polk. High Wind Warning until 2 PM EDT Thursday for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Southeast Monroe-Unicoi. VA...NONE. && $$
Area Forecast Discussion
National Weather Service San Francisco Bay Area
852 PM PDT Wed Mar 17 2021 .SYNOPSIS...Light rain will return to the region late tonight into Thursday morning as a weather system approaches. Light to occasionally moderate rainfall will become more widespread Thursday afternoon as a cold front slowly moves southward and inland across the region. While lingering rain showers may be possible into Friday, drying conditions are likely to return and continue into the upcoming weekend. && of 08:51 PM PDT Wednesday...Cloud cover is increasing into the night as the next system approaches the region. The mostly cloudy to overcast conditions will allow for a warmer overnight temperatures with lows in the mostly in the 40s. The main event tonight will be the initial chances for rain moving into the North Bay in the late night. Higher-resolution models and the local WRF place the first few showers in Sonoma Co between 2 to 3 AM and that rain moves into the San Francisco Bay around 5 AM. Rainfall chances look to reach the Santa Cruz Mtns around that time as well and slowly stretch into the Monterey Bay closer to sunrise. Most of the rainfall rates look light through much of the late morning but could increase into more moderate rates into the day. Thursday afternoon offers a stronger band of rain around the Monterey Bay. Some models are showing some local rainfall rates increasing to as much as 0.40" an hour during that time, but confidence isn`t high that these rates will last. While these rates are below debris flow thresholds, this will be something operations will examine closely through the afternoon. Thursday evening`s rainfall will more focused on the northern portions of the Big Sur coast. The HRRR and the local WRF show the potential for rainfall rates reaching 0.30"-0.45" per hour along higher elevations but this doesn`t look to be widespread. Luckily these higher rates do not appear to cross into the Monterey Co burn scars, but again will be something the forecaster team will keep a close eye on. Rainfall rates look to taper off into the late night with light showers remaining well into Friday. The last few lingering rain chances will move east and out of the area Friday evening, leading into another dry trend. Rainfall totals over the next few days remain consistent with what was mentioned in the previous discussion below. && .PREV of 01:46 PM PDT Wednesday...Mid/high level clouds have held temperatures down across the region this afternoon with most locations still in the low/mid 50s. While additional daylight may allow for a few locations in the interior areas of the Central Coast to reach around 60 deg F, this will likely be the exception. Thus, have lowered afternoon temperatures for today by a few degrees. Look for temperatures overnight to be warmer as well given the cloud cover overhead with lows Thursday morning only dropping into the 40s for most areas. The forecast remains on track for light rain to develop over the North Bay and along the coast beginning after midnight and through sunrise as moisture advects inland ahead of an approaching frontal boundary. The latest thinking is that the cold front will drop from north to south across the Bay Area Thursday morning and then down across the Central Coast during the afternoon/evening. Southerly winds will increase over the Pacific tonight ahead of this boundary with breezy to gusty conditions possible along the coast and in the hills into Thursday morning. Wind gusts of 25 to 35 mph will be possible with the higher peaks potentially exceeding 45 mph. By Thursday afternoon, a deeper plume of moisture is forecast to advect inland over the Central Coast as the boundary drops southward. This will likely result in more widespread moderate rainfall over the Santa Cruz Mountains and Santa Lucia Range during the afternoon and evening hours. This said, still not expecting excessive rainfall rates which would trigger debris flows over recent burn areas. Conditions will begin to dry out from north to south throughout the day with lingering rainfall over the Central coast into Thursday night before the boundary finally pushes south of the region. A few showers may linger into Friday morning as well, yet most of the region can expect drying conditions during the day Friday with seasonably cool temperatures. With this forecast update, have lowered rainfall amounts over the North Bay and greater San Francisco Bay Area and increased them from the Santa Cruz Mountains southward. Looking for rainfall totals from Thursday through early Friday morning to range from 0.25"-0.50" for most urban areas of greater San Francisco Bay Area with 0.50"-1.25" in the coastal ranges and Bay Area Hills. There is the possibility that rain shadowed Valley locations such as San Jose may only see 0.10"-0.25". To the south, 0.25" to 0.50" will be likely for most urban areas with upwards of 1.00" for places such as Santa Cruz and hills of the Central Coast. The greatest rainfall looks to occur over the Santa Cruz Mountains and Santa Lucia Range where 1.00"- 2.00" will be possible. Lastly, snow levels at the time of precipitation look to remain greater than 5,000 feet before lowering below 3,000 feet on Friday once precipitation has ended. Thus, snow is unlikely to be a concern with this weather system. Dry weather and seasonably cool temperatures are likely for the upcoming weekend. Overnight conditions will likely drop back into the 30s for many interior locations, yet widespread freezing temperatures are not expected at this time. A gradual warming trend is then forecast to occur during the middle part of next week and potentially into late next week as high pressure builds over the region. The ensembles are in good agreement with the development of this pattern along with dry weather conditions for next week. && of 05:00 PM PST Wednesday...For the 00Z TAFs. Satellite imagery shows an approaching storm system over the eastern Pacific with thickening high clouds arriving from the west and patchy mid level clouds bringing 2500-3500 ft MVFR BKN-OVC cigs near Monterey Bay and similarly heighten few-sct clouds elsewhere. Radar imagery depicts light reflectivity returns arriving with the high clouds in the warm sector but no ground tips have been reported, thus it is falling as virga. With this system, expect breezy to occasionally gusty south to southwest winds, gusts roughly 20-25mph, MVFR cigs and visbys, and wet run ways at times. Precipitation with the upcoming system will be segmented out with the initial rain arriving late Wednesday night into early Thursday morning. A secondary slug of moisture ahead of the primary cold boundary will bring potentially mod to briefly heavy rain for the Santa Cruz mountains regions beginning midday Thursday afternoon before transitioning to focus on the Monterey Bay terminals by late Thursday afternoon through Thursday evening. Vicinity of KSFO...VFR with FEW to SCT at 2500 to 3500 ft this evening as well as lowering/thickening high clouds at 15000 feet. Winds will gradually weaken and back towards the south overnight then increase to become breezy with occasional gusts 20 to 25mph as the front nears through Thursday. For tonight, expect to see continued VFR conditions until the pre dawn hours Thursday morning as precipitation begins at roughly 12Z. Expect to see some periods of improving conditions through the late morning to early afternoon before another round of precipitation arrives Thursday evening. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...Intermittent MVFR/VFR cigs through the night, ie SCT-BKN, becoming OVC by the predawn hours of Thursday morning. VCSH/-SHRA will begin around 12Z, accompanied by lower MVFR cigs with occasional vis drops. Gusty S/SE winds for KSNS around 12Z lasting through the period. A second slug of rain arrives later Thursday and could bring borderline IFR/MVFR conditions with mod to briefly heavy rain into the evening. && of 08:47 PM PDT Wednesday...A storm system will move across the coastal waters between late tonight and through the day tomorrow. Southerly winds ahead of the front will increase overnight, becoming breezy through the night, then strengthening further to become moderately gusty, ie 25 to 30 kts, occasionally up to 35 kts, by the predawn hours Thursday morning as the front nears. Data indicates peak winds along the immediate coast will occur through the sunrise hours then gradually taper off through the day as the front pushes inland. These winds will generate locally steep fresh southerly swell of roughly 8 feet at 8 to 10 seconds, creating hazardous conditions for small craft vessels near the front. Otherwise, a light northwest swell today will be replaced by a larger northwest swell of roughly 12 to 16 feet at 15 seconds on Friday. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM SCA...Pt Arena to Pt Reyes 0-10 nm from 9 PM SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM && $$ PUBLIC FORECAST: RGass/Murdock AVIATION: DRP MARINE: Dhuyvetter Visit us at Follow us on Facebook, Twitter, and YouTube at:
Updated for aviation forecast discussion.

&& .SHORT TERM...(Tonight through Friday night) Issued at 331 PM CDT Wed Mar 17 2021 The enhanced risk of severe storms continues unchanged for areas generally south of a Van Buren Missouri to Hickman Kentucky line. That said, the prospects for bonafide surface-based instability are dwindling. The warm front is just south of KMEM and arcs northwest into northwest Arkansas. The southerly winds and some tangible SBCAPE will eventually work eastward into southeast Missouri late this evening, but by then the mid and upper flow will back to nearly due south which makes it difficult to have any significant shear to organize convection. The latest HRRR indicates that we may see a few hours of relative dry weather through 00Z as the current area of rain continues northeast out of the area by 00Z. We are still expecting our next round of showers and some storms to sneak up into southeast Missouri around 00Z. This area is still expected to be elevated and instability will continue to be meager. This area of convection will push northeast through the evening with the same general weakening trend we have seen with the two rounds so far today. We will keep an eye on the environment this evening, but severe weather is not looking very likely at this time. As for the Flash Flood Watch, we will let it ride. It captured the heaviest rains from earlier today, and they overlap the 1" additional QPF through tonight. Any flooding should be very isolated over southeast Missouri and southern Illinois. Am somewhat concerned for the southern Pennyrile, where over an inch of rain will be possible tonight, but they did not have nearly as much earlier today. The upper low will move east over the region Thursday. Cannot completely rule out a rumble of thunder with it, but will settle for just mentioning showers. As the surface low passes by just to our north Thursday afternoon, strong north winds will bring much cooler air into the region Thursday night. Any lingering showers are expected to be done by midnight, so there is no wintry concern at this time. However, temperatures may reach freezing by daybreak Friday over much of southern Illinois, so if the showers linger into the overnight hours we may need to re-evaluate the wintry potential. Despite plenty of sunshine on Friday, it will be much cooler with highs only in the lower 50s. Much of the region may drop to freezing Friday night with clear skies, light northeast winds, and dewpoints well into the 20s. .LONG TERM...(Saturday through Wednesday) Issued at 331 PM CDT Wed Mar 17 2021 Surface high pressure will be centered over the northeast U.S. this weekend as an upper level ridge builds over the middle Mississippi and lower Ohio valleys. This will keep the PAH forecast area dry Saturday through Monday. Temperatures will be near seasonal Saturday and Saturday night with easterly winds, then winds will become southerly by Sunday, resulting in gradually warming temperatures Sunday and into the early part of the work week. By Monday night, models show a surface low over the Central Plains. This low will move slowly northeast due to the surface high pressure and upper level ridging over the eastern U.S. Models are generally on the same page and take the surface low northeast into the upper Mississippi valley by Wednesday. At this point, model blends bring showers into far western portions of the PAH forecast area Monday evening, with chances spreading slowly east across our entire region by midday Tuesday. Good chances of showers will continue across our entire area Tuesday afternoon into Tuesday night as the cold front moves across the PAH forecast area. Some of the slower model solutions take even longer to get the front through our area, and the blends account for this by lingering slight chances for showers into Wednesday. Due to various models timing differences with the movement of the front, confidence is too low to include any thunder at this point. As models come to better agreement, we could see some thunderstorm potential across at least southern portions of our region at some point. Temperatures will remain above normal into mid week as winds continue from the south. && .AVIATION... Issued at 633 PM CDT Wed Mar 17 2021 After the afternoon convection finally moved east of the area, more showers and storms have already moved into parts of southeast MO as of this writing. This will be the trend as we head into the evening hours. The activity impacts southeast MO and far west KY early in the period, will pivot northeast and impact the rest of the terminals later this evening and overnight. There may be a brief lull period as a sfc low moves across the area. However, scattered showers will gradually return to the area Thursday. Cigs will be MVFR in the convection and likely stay that way for the majority of the period, except for possibly in that lull period. Winds will be southeasterly but go through several changes in direction as the surface low passes across the area overnight tonight and into tomorrow. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...Flash Flood Watch through Thursday morning for ILZ075-076- 080>082-084>086-088>090-092>094. MO...Flash Flood Watch through Thursday morning for MOZ076-086-087- 100-107>112-114. IN...None. KY...Flash Flood Watch through Thursday morning for KYZ001>006. && $$
...Update to aviation forecast discussion...

.DISCUSSION... Issued at 358 PM CDT Wed Mar 17 2021 A strong and dynamic system is expected to bring more rain, wind, and even some snow to the area, resulting in an active next 18 hours or so. The upper low has been progressing northeast and is currently over OK as of 2030Z, while the sfc low has been deepening throughout the day and is centered over OK/AR at 1000mb. This leaves eastern KS on the northwest side of the system with CAA and cloudy, misty conditions keeping temperatures in the upper 30s to low 40s across the CWA - not really having a chance to warm up much today. The next batch of rainfall is on its way from southern and central KS and should become more scattered to widespread across northeast and east central KS later this afternoon and especially this evening. As the upper low continues to lift northeast, colder air aloft wraps around the back side of the system and results in more CAA, turning rain over to snow from west to east overnight. What makes this particularly concerning is this snow potential exists during periods of stronger forcing with increasing mid-level frontogenesis within the deformation zone. Hi-res models are picking up on snow banding more easily than the GFS, as can be expected, but given the potential for this set-up to produce snow amounts of 1-3 inches, felt it was worth issuing a winter weather advisory for areas along and southeast of a line from Council Grove to Topeka. Would not rule out some locally higher amounts as well, which can be seen from SREF plumes showing a mean of 3-3.5" for Topeka and Emporia. Little to no accumulation is expected for areas northwest of the advisory. Additionally, the strong pressure gradient puts us in a position to see near advisory-level winds, although guidance varies on this potential to some extent as well. The HRRR would suggest seeing wind gusts around 40-45mph, whereas the RAP is not nearly as aggressive and other guidance gives gusts around 35mph. Still, these kinds of winds with wet snow are enough to present a concern for reduced visibilities, which would also cause travel impacts. It should also be mentioned that with surface temperatures so close to the freezing mark and the colder air aloft, just a few degrees difference in temperature will be crucial to whether certain areas see more rain vs snow during the overnight hours. As we head into the early morning hours of Thursday, also can`t rule out some freezing drizzle or drizzle on the back edge of the system as we lose saturation in the vertical profile, and therefore lose cloud ice. As a whole, however, temperatures should warm up enough through the morning and the better forcing should move far enough east after sunrise to see diminishing impacts after the morning commute. Temperatures should reach the 50s in the afternoon for most, except perhaps the far east central areas which may see lingering drizzle and cloudiness further into the day. An upper ridge moves into the area late this week, bringing a return to warmer and drier conditions to round out the work week and enter the weekend. We see a return of temperatures in the 60s by Saturday and lasting into next week, with the next upper trough bringing the next chance of rain possible on Monday. However, differences in timing between the models keeps low chance PoPs into Tuesday/Wednesday. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 632 PM CDT Wed Mar 17 2021 Rain showers will continue to increase over the evening hours. This rain will likely mix with or change over to snow for a time, especially at KTOP/KFOE, before gradually ending by early morning. MVFR and IFR visibility reductions are likely within the precipitation, especially in any heavier snow. Ceilings will continue to hover around the MVFR to IFR border overnight, gradually rising to MVFR and eventually VFR during the day tomorrow. Winds will remain northerly, sustained at 15 to 20 kts and gusting 25 to 35 kts. && .TOP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 10 PM this evening to 9 AM CDT Thursday for KSZ026-037>040-054>056-058-059. && $$ DISCUSSION...Picha AVIATION...Reese