Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/15/20


Area Forecast Discussion
National Weather Service Gaylord MI
1045 PM EDT Tue Apr 14 2020 .UPDATE... Issued at 933 PM EDT Tue Apr 14 2020 Broad cyclonic flow...cold air aloft and wrap-around moisture continue to produce sct/nmrs snow showers across the Western Great Lakes region late this evening. Another weak wave/convergence axis is making its way into Northern Lower Michigan attm...resulting in an uptick in ongoing snow shower activity. Meanwhile...another wave/convergence axis is pivoting thru Lake Superior toward Eastern Upper Michigan...also resulting in an enhanced line of snow showers. Latest RAP suggest the Northern Lower Michigan wave will slide thru our area over the next few hours...exiting our CWA late tonight. Near term models show the Lake Superior wave will drop into Eastern Upper Michigan overnight and will stall over that area for a few hours. Have made some upward adjustments to POPs and to snow amounts overnight...and have extended the Winter Wx Advisory for Chippewa county thru 12Z Wednesday with another 2 inches or so of new snow expected for some locations. && .NEAR TERM...(Through Wednesday) Issued at 331 PM EDT Tue Apr 14 2020 ...Snow shower focus shifting to eastern upper... High Impact Weather Potential: Locally intense snow showers thru this evening, especially in parts of eastern upper MI. Low pressure over nw Quebec continues to move to the ne, while ridging into the OH Valley is edging northward. Plenty of cool and moist low-level air is in place, with steep lapse rates already present this morning per the 12Z APX sounding. When combined with strong mid- April sun, we get widespread cumulus and plenty of convective showers. In northern MI, we also have lake and synoptic contributions to clouds/precip, resulting in something of a mess. In particular, we have seen a series of surface trofs and wind shifts proceed across the area. One in particular has hung up over eastern upper MI, with resulting persistent and considerable low- level convergence. We presently have sw winds on Beaver Isl, wsw at Mackinac Isl, and were for time almost south at DeTour. But across central and northern Chippewa Co, nw winds are present. This is focusing a lot of convergence over far eastern upper MI (that convergence is weaker to the west, with westerly winds at Newberry and points west). There has been a substantial uptick in snow showers as a result, somewhat hidden from view given how far that area is from local radars. But Kinross has seen vsbys below 1SM for over 90min now, dipping to 1/4SM at times (including presently). So the expectation is for convergence-forced training showers, of the sort that could produce flash flooding in the warm season. Except of course that we`ll be getting snow instead. HRRR/Rap runs today have pretty consistently shown a potent QPF max this afternoon and evening in central Chip Co, somewhere between Rudyard and Sugar Isl. Most recent Rap has a max of almost 0.50" QPF near southern Sugar Isl. HRRR is closer to Kinross, at nearly 0.75". Will not go quite /that/ bonkers, though higher local accums are certainly possible. Snow-liquid ratios in the high teens will result in a (conservative?) forecast of 4 to 8" of accums this afternoon and evening, from Trout Lk to Rudyard to Neebish/Sugar Isl. In northern lower MI, best activity presently is focused from Charlevoix Co to sw Presque Isle Co. This is along another axis of low-level convergence. Can`t have convergence everywhere of course, and other parts of northern MI are seeing a relative lull (though diurnal affects are still sustaining some showers). Plan for numerous snow showers to be sustained thru the night in far northern lower MI, especially south of PLN and north of Kalkaska. But loss of diurnal instability should take a little bit of intensity away. Will maintain the current northern lower MI advisory I suppose (it expires at 7 pm), but most accums tonight will be less than 2 inches. Given prevalent lake instability, some locally higher amounts are certainly possible. For Wednesday, inversion heights are slipping lower as 500mb heights rebound behind the shortwave that is helping things tonight. We do still have cool/moist low levels, a high sun angle, and at times cyclonically curved flow (especially in northern sections). The above will support nw-flow lake effect off of Superior initially (with the main focus from Alger into far western Mack Co). Diurnal components will broaden precip chances with time, much like today, but again less intense. Suppose a stray inch or two is possible, mainly in eastern upper MI. Chilly min temps tonight, mainly upper teens to lower 20s. Mid 30s to around 40f for highs Wednesday. && .SHORT TERM...(Wednesday night through Friday) Issued at 331 PM EDT Tue Apr 14 2020 High impact weather potential: Minimal, although a few snow showers continue to remain possible at times into at least Thursday. Pattern synopsis/forecast: Large scale, unseasonable cool upper level troughing is expected to remain in place for the foreseeable future across the Great Lakes region. Primary focus revolves around marginally supportive lake effect parameters combined with smaller scale shortwaves embedded in aforementioned parent troughing that may give a small boost to overall precip chances from time to time through the forecast period. Primary forecast concerns/challenges: PoPs and temperature trends. Initial thermo parameters Wednesday night remain marginally supportive for lake effect snow development given delta Ts of right around 13 C leading to lake induced CAPE values of several hundred J/kg. However, limited synoptic support aloft behind a quick-moving mid-level shortwave, lots of low-level dry air and sinking inversions heights should prove to be enough to keep any new snow showers Wednesday night rather isolated and confined to primarily west-northwest flow snow belts of E upper/NW lower. Not much in the way of accumulation...perhaps a few spots pick up a new coating overnight. Overnight lows have the potential to vary greatly across the forecast area given light winds combined with a difference in cloud cover. "Warmest" spots expected to be nearest the Lake Michigan shoreline under more frequent clouds...ranging from the mid- upper 20s. Some locations across the eastern half of the forecast area and over parts eastern upper should easily tumble into the upper teens, if not a bit further assuming less frequent cloud cover. A similar story for Thursday, but with even more dry air to overcome in the low levels per model soundings. Still expect a few snow showers to dot the map from time to time, but expect that they`ll transition from lake effect nature to more convectively driven given cold air aloft leading to impressively steep mid-level lapse rates. Wouldn`t be surprised to see any of these showers contain more of a snow/graupel mix, but again with little in the way of accumulation given a lack of coverage and an increasing mid-April sun angle. One thing of note for late in the day Thursday is a more robust shortwave passing by north of the international border - suppose this could briefly bring an uptick in snow shower coverage across the UP along with the chance of a minor accumulation. Afternoon high temps expected to be some 15 or so degrees below normal at many sites across northern MI...ranging from the upper 30s to near 40 degrees. Slightly warmer H8 air expected to spread atop the region to wrap up the work week in advance of a compact area of low pressure progged to pass through the mid-MS Valley into the Ohio Valley. Suppose the chance for a rogue rain/snow shower isn`t zero, have opted to keep the forecast dry through this time frame for now. Highs boost a few degrees for Friday...generally in the 40s area-wide. .LONG TERM...(Friday night through Tuesday) Issued at 331 PM EDT Tue Apr 14 2020 High impact weather potential: Minimal for now. A brief reprieve anticipated at the start of the extended on Saturday as troughing aloft briefly breaks down, allowing temperature to climb back to near normal for most (generally in the 50s). Trends beyond that would suggest cooler air pours back into the region to wrap up the weekend into the start of next week (along with occasional precip chances) behind a cold front tied to low pressure that treks across southern Canada. Long range guidance toward the end of the forecast period and beyond show at least some positive signs for those looking for warmer spring weather as cold air looks to retreat northward, although that`s plenty off in the distance, so there`s certainly time for that to change. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1045 PM EDT Tue Apr 14 2020 Broad cyclonic flow...cold air aloft and low level moisture will continue to produce sct/nmrs snow showers across Northern Lower Michigan thru Wednesday night...especially across far Northern and NW Lower Michigan where some lake enhancement will be present. Prevailing VFR conditions will occasionally drop of MVFR/IFR within some of the heavier snow showers. West wind AOB 10 kts overnight will strengthen to 10 to 20 kts with some higher gusts on Wednesday. && .MARINE... Issued at 331 PM EDT Tue Apr 14 2020 Low pressure over northern Quebec will continue to move away from the region, allowing weak high pressure to build into the southern Great Lakes. Gusty westerly winds will tend to diminish with tim thru tonight, and ongoing advisories will be spun down as well. Those winds (w to nw) will get a little breezier again late Wednesday afternoon. && .APX WATCHES/WARNINGS/ADVISORIES... MI...WINTER WEATHER ADVISORY until 8 AM EDT Wednesday for MIZ086-087. LH...NONE. LM...NONE. LS...NONE. && $$ UPDATE...MR NEAR TERM...JZ SHORT TERM...MG LONG TERM...MG AVIATION...MR MARINE...JZ
Area Forecast Discussion
National Weather Service Charleston SC
1154 PM EDT Tue Apr 14 2020 .SYNOPSIS... High pressure will gradually build in from the northwest through late week. Unsettled weather is then likely late week through early next week as several disturbances move through the region. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 1150 PM: KCLX indicated a cluster of showers and isolated thunderstorms across the GA and lower SC waters, moving NE at 30-35 kts. Isolated showers were also tracking across McIntosh Co. Latest HRRR indicate that the convection will remain over the waters for a few more hours, then develop west over the coastal areas late tonight. Based on radar trends and latest guidance, I will adjust PoPs through the rest of the night. Temperatures appear on track to cool into the upper 50s to low 60s by daybreak Wednesday. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Moderate confidence through the period that a stalled front offshore Wednesday will turn into a cold front and push to the southeast farther away from the area as high pressure builds from the northwest. The combination of deep moisture and upper lift from a jet and possible shortwave energy will yield showers around daybreak Wednesday, especially near the GA coast, followed by drying from the northwest during the day. Could be a few thunderstorms near the coast as well with even an outside chance of a strong to possibly severe storm, especially near the GA coast and over the nearby Atlantic. Most of the rain should be offshore Wednesday evening as cooler and drier high pressure builds from the northwest and continues through Friday. However, moisture will be returning Friday with the high situated offshore and return flow in place, and can`t rule out a few showers during the afternoon, mainly in GA. Otherwise, temperatures will modify through the period but still likely to remain below normal. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... A cold front could bring scattered showers and tstms to the area Friday night and Saturday. Another system may bring a wave of showers and tstms through the area late Sunday afternoon through Monday. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/... 00Z TAFs: A cold front will move through the area overnight with winds veering to the north toward daybreak and surging a bit. VFR conditions will become MVFR, possibly even IFR, ceilings develop mainly after 06Z and lasting until about 15Z at KSAV and about 18Z at KCHS. Extended Aviation Outlook: High confidence in VFR conditions through Friday with an increasing risk for periodic restrictions starting Friday night due to low clouds, showers and possible thunderstorms from a stalling cold front over or near the area. && .MARINE... Tonight: A cold front will shift through with south/southwest winds veering to southwest, except more westerly at the coast late. Seas should average 2-4 feet through tonight, with some 5 footers 40-60 nm offshore. Wednesday through Sunday: High confidence through Friday night with high pressure building into the area and remaining until a cold front begins to approach Friday night. Low confidence this weekend as much depends on the placement of the front over or near the area. Marginal Small Craft Advisory conditions will be possible near the Gulf Stream Wednesday across the Charleston nearshore waters and offshore GA waters but probably more likely over the offshore waters Wednesday night/Thursday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM... LONG TERM...JRL AVIATION... MARINE...
Area Forecast Discussion
National Weather Service Des Moines IA
635 PM CDT Tue Apr 14 2020 .DISCUSSION.../Tonight through Tuesday/ Issued at 300 PM CDT Tue Apr 14 2020 GOES-East clean IR imagery shows a deep and expansive trough across much of the CONUS with northerly flow over the western US that becomes from the southwest over the northeastern US. Some cloud enhancement over the North Dakota - South Dakota border is associated with a PV anomaly that has started to influence our weather this afternoon and will do so tonight as well. The day starting off with plenty of sunshine that allowed the surface to warm relatively speaking. With cold air in the mid-levels fostering steep low level lapse rates, shallow cumulus clouds developed once again by mid to late morning. With these clouds and saturation in the dendritic growth zone (DGZ), have seen spotty snow showers similar to yesterday, though more so over northern Iowa versus farther south over central Iowa. Over central and southern Iowa, there has been more more subsidence keeping the forecast dry there. Similar to yesterday as well as last Thursday, these spotty snow showers can bring brief reductions in visibility with Mason City dropping to 3 miles around 1pm. In addition, these showers can bring down stronger wind gusts from aloft with peak gusts in the 30 to 40 mph range so far this afternoon. The aforementioned PV anomaly will reach Iowa in the cyclonic flow this evening with associated 1-3km QG convergence increasing over the state. Soundings at LWD and OTM and cross sections through southern Iowa maintain quite a bit of dry air in the lowest 1.5km or so with saturation above this and lift within the DGZ. This should allow for a few to several hour period of light snow. The HRRR and RAP both maintain largely subsidence within the saturation while the coarser grid models are showing more lift within the saturation. Overall, message is that accumulations should be south of Highway 34 and less than an inch. As surface high pressure slides into the region from the northwest on Wednesday, should have a break from the afternoon spotty snow showers as soundings show less saturation and overall subsidence. During this time, a more significant shortwave trough will begin to dive down the backside embedded within the longwave trough over the western US and move over the central Rockies by midday Thursday. A baroclinic zone will set up south of the state with isentropic lift increasing on the 295K surface. As saturation deepens with broad scale lift maximized over far southern Iowa into Missouri, will see precipitation spread over southern third of the state up to around I-80 or so. Soundings at CSQ, LWD, and OTM show much of the profile below freezing with the exception of the lowest 500 to 1000 feet with the wet bulb zero temperature near or slightly above freezing during the day. So precipitation may waver from initiation to daytime to nighttime between rain and snow. With precipitation expected over southern Iowa, have continued the trend of lowering highs back into the upper 30s, which may still be too warm in the end. Any accumulation during the daylight hours would likely be confined to grassy or elevated surfaces. Temperatures will lower below freezing in the evening with temperatures and wet bulb temperatures around 30 degrees or the upper 20s. This should allow for some accumulation, even perhaps on roadways, before subsidence spreads into the state by 12z Friday. Total accumulations from Thursday to Friday morning could be around an inch to two inches near the Missouri border with a slightly higher band near or south of 136 Highway in Missouri. High pressure will pass south of the state Friday into this weekend with dry conditions and milder air returning over the region this weekend into perhaps early next week. This will bring the first near normal temperatures in a week to most places in Iowa. There could be another cool shot after Monday, though this should be more short-lived rather than a week-long cool episode that we are currently in if it comes to fruition. The GFS and CMC, supported by a negative trending Arctic Oscillation, would support this cool shot while the ECMWF would support highs above normal. && .AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/ Issued at 635 PM CDT Tue Apr 14 2020 Light snow is expected across the southern third of Iowa late this evening into the early morning hours. This will produce MVFR to IFR ceilings and visibilities, mainly affecting KOTM tonight. This system will quickly depart by daybreak on Wednesday with VFR conditions returning to southern Iowa. Elsewhere, VFR conditions are expected for the duration of the forecast with winds becoming light overnight and then increasing from the northwest on Wednesday as mixing deepens. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...Ansorge AVIATION...Cogil
Area Forecast Discussion
National Weather Service Goodland KS
528 PM MDT Tue Apr 14 2020 .SHORT TERM...(This evening through Wednesday night) Issued at 125 PM MDT Tue Apr 14 2020 Satellite imagery and 500mb RAP analysis showed weak northwesterly flow over the High Plains today, with a trough over the Upper Midwest. A layer of cumulus clouds developed across the region this afternoon as northwest winds blew at 15 to 25 mph, with gusts around 35 mph. At 1:00 PM MT, temperatures ranged in the upper 30s to upper 40s. Northwest flow continues aloft tonight as temperatures fall into the low to mid 20s. Winds relax through the evening, becoming westerly at 10 mph or less under partly to mostly cloudy skies. A strong shortwave digs south into the central Rockies on Thursday, with a surface low developing in eastern Colorado. Flow aloft becomes zonal with winds around 10 mph or less at the surface, mitigating fire weather concerns. Temperatures reach the mid 50s to low 60s for highs. Cloud cover increases as rain chances move into the region from the northwest Wednesday evening, changing to light snow overnight as temperatures fall into the 20s. Snow amounts of a half inch or less will be possible for locations along and north of the Nebraska border through sunrise. However, additional light snowfall is anticipated Thursday and Thursday night. .LONG TERM...(Thursday through Tuesday) Issued at 222 PM MDT Tue Apr 14 2020 Winter weather and the potential for elevated fire weather conditions are the main concerns in the extended forecast. A surface low over Southwestern Kansas and Southeastern Colorado will progress east Thursday morning across the lower half of Kansas. A cold front will drop through the region from the north. Breezy conditions are expected with northerly winds coming in behind the front. High temperatures will range from the mid-30s in the northwestern part of the CWA to the mid-40s in the southeastern part of the CWA. Timing of the cold fropa will be key in determining high temps. Looking at thermal profiles, this appears to be mainly a rain/snow event. Expected snow totals have shifted southward a bit with higher amounts expected to extend along the I-70 corridor. This is due to the expected placement of the front and where the best frontogenesis lies. Relatively warm ground temperatures will aid in initial melting of snow as it begins to fall, resulting in less overall accumulations. Precipitation will continue through the overnight hours and into early Friday morning. Overnight lows will dip into the 20s. Friday will be a warmer day with highs ranging from the mid-40s to low 50s across the region. The region will come under southwest flow aloft as a split in the overall flow pattern occurs. A weak shortwave trough will move through the region Saturday evening, however, conditions will remain dry. Above normal temperatures are forecasted for Saturday through Tuesday as a gradual warming trend brings us into the 70s by Tuesday afternoon. Through this time, elevated fire weather conditions may be possible. Relative humidity values will range from the mid-teens to low 20s across the southwestern part of the CWA. Winds will not be near criteria. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 525 PM MDT Tue Apr 14 2020 VFR conditions are expected throughout the TAF period at both KGLD and KMCK. Winds will generally be from the northwest Tuesday evening with gusts to 20-25 kts quieting down after sunset. Light and more variable winds are expected overnight. Light westerly winds will continue Wednesday morning through Wednesday evening. Scattered clouds are expected at around 10 kft for most of the TAF period. These clouds will begin to thicken and lower Wednesday evening as precipitation chances increase into the overnight hours tomorrow night. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ SHORT TERM...JBH LONG TERM...AW AVIATION...PATTON
Area Forecast Discussion
National Weather Service Grand Rapids MI
738 PM EDT Tue Apr 14 2020 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 330 PM EDT Tue Apr 14 2020 - Cold tonight with snow showers - Gradually warming this week but still cool && .UPDATE... Issued at 609 PM EDT Tue Apr 14 2020 I have updated our forecast for this evening into the day on Wednesday by expunging all mention of rain showers in favor of snow showers since the wet bulb zero is on the ground through Thursday morning. Also,I increasing the pop to likely this evening and to a high chance overnight. I have noted over the past 40+ years of forecasting that at this time of year, just because you have high temperature of 40 degrees, if you have dew points in the teens or 20s (which it is today and will likely be tomorrow), when a shower moves overhead, it just snows. That is because the snow flakes cool to the wet bulb temperature, which is below freezing so you do not get rain. The showers overhead are convective and some will have briefly moderate snowfall rates associated with them. Driving to work around 330 pm this afternoon I drove through a snow shower with 1/2 mile visibilities. We just had a similar snow shower at the office (not has heavy on ASOS ). The latest run of the RAP model has equilibrium heights for convection this evening to 14000 ft, with around 100 j/kg of cape. That is decent for snow showers actually. There is the snow showers this evening then there is a system largely passing south of us Wednesday morning, but the snow showers from that may get as far north as I-96 based on the latest run of the RAP model and that also fits well with HREF 6 hour probability of .01" forecast which is 60 to 70 pct between 8 am and 2 pm near and south of I-96. So I increased the pop for Wednesday to more so allow for the snow showers to get farther north into our CWA Wednesday. && .DISCUSSION...(This evening through next Tuesday) Issued at 330 PM EDT Tue Apr 14 2020 -- Cold tonight with snow showers -- The main concern is whether temperatures will reach the mid to lower 20s in the growing belts, which may begin to damage to some crops. Some models suggest the near-surface layer decouples overnight and winds become nearly calm for a period, allowing for radiational cooling. While below-freezing temperatures are likely, an anomalously deep freeze for this point in the season does not appear to be in the cards downwind of Lake Michigan. There is a shortwave trough approaching with a slight amount of 850 mb cold advection overnight which may support the maintenance of stratocumulus and scattered snow showers overnight. Water temperatures in the low 40s at the Port Sheldon and South Haven buoys suggest continued mixing of the boundary layer overnight at least near the lake, with lake-effect clouds possibly maintained despite a dry air mass. Winds 10-15 mph are available at 1000 to 2000 feet to be mixed to the surface if decoupling does not occur. Early this morning, quick moderate bursts of snow between Grand Rapids and Big Rapids created slick spots and travel slowdowns along US-131. It is possible to see a repeat of that tonight, with no particular area completely safe from a light snow accumulation. -- Gradually warming this week but still cool Ensembles are in good agreement of cold, freezing temperatures again Wednesday night with an isolated snow flurry. Slightly milder temperatures are expected Thursday through Saturday, with solutions increasingly diverging thereafter. Southern Michigan (Kalamazoo-Jackson and south) is at risk of accumulating snow on Friday from isentropic lift, but the greater risk is down in Indiana. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 739 PM EDT Tue Apr 14 2020 A weak cold front is moving toward southwest Lower Michigan this evening. It has come convective instability associated with it. We are seeing most unstable cape values near 100 j/kg with lapse rates near 7c, which is impressive for snow showers actually. I have seen some of our TAF sites, like LAN, which observed 1/2SM SHSN at 2253z. That is typical for convective snow showers to have the visibility go from P6SM to below 1SM in a short time only to come back quickly to P6SM. Our radar continues to show convective snow showers across Lake Michigan into western WI. The weak cold front pushing these snow showers along should move on shore by 06z. That should end the snow showers for our TAF sites this evening. However, that is not all we are watching, there is a trailing shortwave and surface low on the front that brings an isentropic lift event into our southern CWA Wed morning. We could see 4 to 6 hours of light snow for the I-94 TAF sites (IFR conditions) from say 09z to 15z (give or take a few hours). Once that moves through all of the CWA and all TAF sites should clear as much drier mid level air moves in. The bottom line is mostly VFR but brief periods of IFR are possible till 06z at most of our TAF sites. It should mostly be VFR between 06z and 09z. Then the I-94 TAF sites could see IFR in snow from 09z till 15z. All sites should be solid VFR by 18z and winds will be lighter than we have seen in the past few days. && .MARINE... Issued at 330 PM EDT Tue Apr 14 2020 Waves 4 to 5 feet were observed at the Port Sheldon buoy during the 2 PM hour, but the trend in winds and waves will be downward this evening. Still, it will be choppy, with 2 to 4 foot waves expected tonight. The next chance of conditions hazardous to small craft will be Thursday morning. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ UPDATE...WDM DISCUSSION...CAS AVIATION...WDM MARINE...CAS
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1129 PM EDT Tue Apr 14 2020 .UPDATE... Issued at 1113 PM EDT TUE APR 14 2020 Turning into a bit of a tricky forecast for the overnight. Snow has moved out, but the moisture left behind, along with light winds and cooling temps, has led to some fog across portions of eastern Kentucky...including here at the office. However, the high clouds are continuing to move out, and the center of a high pressure system is now parked over central Kentucky. With the high already built in, we may not be advecting much more of the dry air into the eastern Kentucky. As a result, the expectation now is that fog may first develop across portions of the far SE where snow impacted the latest (basically JKL SEward) and therefor haven`t had a chance to dry out, and as temperatures continue to cool below freezing, this fog will transition to a frost instead. Meanwhile, observed temps at 10pm were considerably lower than forecast thanks to the cooling impact of the snow, with some sites already at or close to the forecasted nightly lows. With really no model guidance having a handle on this, manipulated lows and the overnight diurnal curve by hand. That being said, though the trend is in the right direction considering the pattern in place and the decoupling that is likely to happen, there may end up needing to be some more updates throughout the night as more observations come in, especially in the deeper valleys. UPDATE Issued at 615 PM EDT TUE APR 14 2020 A pretty potent band of snow has set up and is moving SE. Despite moving into 40 degree air, the colder air aloft has been able to overcome, and mostly snow is being seen along with quickly falling temps. Tried to better show the current status of this snow band location in the pop/weather grids, and transition that band to the SE over the next few hours. Also increased snow amounts in some locations, especially the higher terrain, where between a tenth and a half an inch of snow cannot be ruled out. May have snow lingering a bit too long in the far SE as we head into the overnight, so will continue to monitor and update here as needed over the next couple hours. The good news is that we are still warm enough on the ground that after the heaviest band of snow moves out, much if not all of the snow should begin to melt off throughout the rest of the evening. In addition to these changes, also updated the near term forecast for temps and winds based on the current observations. As noted, temps are quickly dropping along the band of snow, but may recover a bit on the backside after the band moves out, before the sun sets. This too will help to allow any snow accumulations to melt. && .SHORT TERM...(This evening through Wednesday night) Issued at 405 PM EDT TUE APR 14 2020 19z sfc analysis shows high pressure edging into the state from the west while cyclonic flow remains in place over the east. An active pattern aloft is pushing an impulse through the area this afternoon. As a result, plenty of clouds are found over the state along with a few bands of light pcpn. With such cold temperatures aloft some of this pcpn is falling as light snow over our northwest fetches. The snow is capable of making to the sfc even though temperatures are in the upper 30s and lower 40s north but in the low to mid 40s southeast. Meanwhile, with northwest winds of 5 to 10 mph dewpoints varied from the mid 20s north to the mid and upper 30s in the southeast. The models are in decent agreement aloft through the short term portion of the forecast. They all depict a very deep trough through the Great Lakes and into the Ohio Valley with bands of energy rotating through its base. The first of these washes over eastern Kentucky this evening and early overnight with even a drop in heights. Another heads this way later Wednesday, though the trough will be relaxing by that time so that heights actually start to rebound by dawn, though northwest flow will continue. Given the limited model spread with these features have favored the NBM as a starting point for the grids with some adjustment towards the HRRR and NAM12 on details. Sensible weather will see spring`s bite tonight with an evening of some flurries giving way to clearing skies and falling temperatures. As a result, freezing temperatures are expected nearly everywhere by dawn along with widespread frost. Accordingly, a Freeze Warning is in effect for eastern Kentucky into Wednesday morning. Temperatures will see only a limited rebound on Wednesday, but still nearly 10 degrees warmer than afternoon temps today. Sky cover will be more variable through the short term making forecasting these temperatures a bit of a challenge given uncertain solar radiation during the day and likewise the black body night time radiation. However, it does look cold enough for some pockets of near freezing temperatures by Thursday morning and areas of frost - albeit somewhat dependent on the cloud cover. The main question will be if that next batch of upper energy will be enough for some showers for our northern counties Wednesday evening. For now, have allowed a small chance generally north of the Mountain Parkway as a secondary cold front drops into the state. Did not make much in the way of adjustments to temperatures from the NBM through the period given the uncertainty with cloud cover interfering with a potential ridge to valley split night Wednesday night into Thursday morning. As for PoPs, ended up on the high side of the NBM numbers this evening and again later Wednesday into that night with a bit of a lean on the more `wet` NAM12. .LONG TERM...(Thursday through Tuesday) Issued at 300 PM EDT TUE APR 14 2020 A fairly active weather pattern is on tap for the extended. A series of weather systems will bring repeated chances of rain to eastern Kentucky from Thursday night through Monday. Only light rain is expected at this time across the area. The period will start off a bit cold, with widespread frost expected across the area early Thursday morning. After that, warmer temperatures will lead to periods of rain and cloudy skies. The best chance for rain will likely be Friday and Friday night, as a slow moving frontal boundary moves through the region. Another good shot of rain will be possible Saturday night through Sunday, as a second front moves through the area. This second round of rain should end by the end of the day on Monday, giving way to clearing skies and dry conditions Monday night. Temperatures should generally be warm, with daily highs in the 50s and 60s and nightly lows mainly in the 40s expected. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) ISSUED AT 1129 PM EDT TUE APR 14 2020 Update to previous discussion: As snow moved through and then exited, temperatures cooled quite quickly. This has coupled with lingering moisture and KSJS and KJKL and points SE, which were the hardest hit sites by the snow, to create a fog deck. Meanwhile, high pressure has built in overhead, with much much drier air located across the central portion of the state. While a large advection of dry air into the east is not expected, just a little would be enough to break this fog apart and clear the TAF sites...which is what the expectation is at this point. However, climatology is also working against us. Usually with clearing skies and light winds, once fog is in place, we tend to keep said fog. Another added factor is the fact that temps are falling below freezing, and it is also a strong possibility that fog could transition to frost across SE Kentucky. As a result, currently have a forecast that has both KSJS and KJKL clearing out by 5Z...either by drier air, or by transition to frost. But ultimately this is going to have to be a monitor and update if needed situation based on how conditions actually play out through the overnight. A band of decent snow developed across eastern Kentucky late this afternoon and is moving SE and now out of the state at 0Z. This may continue to affect KSJS during the first hour of the TAF period, but conditions are improving. For locations across SE KY within the band, VIS could easily drop to below 1SM and CIGS could drop to LIFR or less. Meanwhile, for the rest of the TAF sites, the band has already cleared the sites and VFR conditions are back in place. The exception is KJKL who is taking a little longer to lift out of IFR CIGS after the snow went through...but should be VFR by 1Z. VFR conditions, including clearing skies and light winds, are then on tap for the remainder of the evening and overnight. A few clouds may move back in from the north during the day Monday, but all precip should remain north of the TAF sites. Predominate winds under 10kts will be out of the WSW by the afternoon Monday, but gusts are forecast between 15 and 20 kts. && .JKL WATCHES/WARNINGS/ADVISORIES... Freeze Warning until 10 AM EDT Wednesday for KYZ044-050>052- 058>060-068-069-079-080-083-084. Freeze Warning from 3 AM to 10 AM EDT Wednesday for KYZ085>088- 104-106>120. && $$ UPDATE...JMW SHORT TERM...GREIF LONG TERM...AR AVIATION...JMW
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
930 PM CDT Tue Apr 14 2020 .UPDATE... 930 PM CDT No major changes in thinking on the period of accumulating snow overnight into Wednesday morning. The main updates were to increase PoPs and snow amounts slightly with northward extent and expand the expected swath of 1-2", locally higher, to portions of our northwest Indiana counties. With temperatures falling to a few to several degrees below freezing and likelihood that roadways are sans residual treatments from the winter, some slippery roadways appear to be a decent bet. With that in mind, opted to issue an SPS from Lee County east-northeastward to all of Cook County and points south. Latest water vapor imagery indicates a well-defined short-wave entering northwest Iowa. In response, radar mosaic indicates a blossoming area of light to moderate snow across central Iowa, extending to a bit north of the Highway 30 corridor. This would seem to favor a northward shift of the initial snow band from the developing f-gen circulation, in line with recent RAP/HRRR runs and the 18z ECMWF. A fairly narrow snow band should overspread northern Illinois I-80 and north after midnight. The best mesoscale forcing in the band will then focusing near and a bit south of the I-80 corridor as the whole band/area of snow gradually drops southeastward. While the air-mass is quite dry, the magnitude of the forcing could support localized amounts potentially in the 2-3" range. The snow will end by mid-day in east-central Illinois and parts of northwest Indiana, possibly mixing with rain before ending. The updates to the forecast inched the 1" line up to the south side of Chicago, with amounts around a half inch perhaps as far north as the far north side of the city. Pavement temperatures in the city according to Chicago snow command were in the upper 30s to mid 40s as of 9pm with air temps still 36-37F, so that may help mitigate road impacts in the city. The swath where amounts in the 1-2" are favored is bounded roughly on the north by a LaSalle-Peru to Joliet to Gary line on the north and a Chenoa to Kankakee to Kouts Indiana line on the south. Within this swath, the aforementioned locally higher amounts are possible. The snow that falls should quickly and fully melt by 10-11am thanks to temperatures warming above freezing and the strong mid April sun. Scattered snow and maybe graupel showers will be possible near Lake Michigan during the afternoon, but no accumulation with temps in upper 30s to lower 40s. Castro && .SHORT TERM... 252 PM CDT Through Wednesday Night... Mother nature is evidently neither satisfied with the winter season, nor paying attention to the date on the calendar, and looks set to deliver a few more chances for snow to the area through the end of the week. For the remainder of the afternoon it`s really what you see is what you get as convective snow (occasionally mixing with graupel) showers continue mainly near and north of I-80 within the core of very cold temperatures aloft with lighter showers farther to the south. In fact, the morning DVN RAOB sampled a 700 mb temperature of about -21C which is squarely at record levels for this time of year. Observations and webcams have confirmed that the heaviest showers have been dropping visibilities to around or just under 1 mile for a few minutes and see no reason that this won`t continue for a few more hours before we lose peak heating. No accumulations are expected but reduced visibilities and gusty winds to 40 mph will be possible under the heavier showers this afternoon. /Tonight.../ The next potential for wintry precipitation (likely all snow) looks to arrive late tonight and may linger through the morning hours on Wednesday with the arrival of a pair of additional mid-level perturbations. These features presently show up in moisture channel loops dropping out of the Dakotas, with a second shortwave emerging across the Central Great Plains and scooting east into Nebraska and Kansas. The latest suite of model guidance supports a coating of snow for locales as far north as I-88, but really moreso towards I-80 and points south where a very narrow corridor of 1-2" amounts is appearing plausible. There is still some amount of uncertainty regarding the exact placement of any `heftier` snowfall totals as is typical with these types of systems and given that there will be at least some modest degree of interaction occurring between these aforementioned shortwaves /PV-anomalies. That said, we are noting a nice degree of run-to- run consistency in the ECMWF which has and continues to show a localized max in QPF immediately near south of I-80 and across parts of the Kankakee River Valley with the rest of the model suite seemingly converging on this scenario as well. From a synoptic/large scale forcing perspective, things look pretty respectable upstairs with an assist from mass divergence under the northwest extent along the cyclonic shear side of a strengthening 150 kt jet streak across the Ohio River Valley along with incoming DCVA from the above-mentioned shortwave. A relatively shallow f-gen circulation is forecast to develop on recent RAP cross sections across the sharpening baroclinic zone which does look to result in at least modest omega into and through the dendritic growth zone late tonight and into early Wednesday morning. Some guidance is very close to developing actual upright convective instability in a small corridor south of I-80 and near I-55/57 during this period, with an attendant notable reduction in saturated EPV* (values near -1 and lower in places which is actually rather robust) at the top of the shallow f-gen circulation. The ceiling on snowfall amounts will likely be kept in check by the rather dry airmass in place with PWATs unlikely to get much above one quarter inch, but it`s not too surprising to see even coarse-resolution guidance developing small pockets of 0.1-0.2" of liquid QPF given everything discussed. snow ratios look to favor something like a 10-13:1 with this activity With this in mind, have gently nudged snowfall amounts up near and south of I-80 and in towards the Kankakee River Valley late tonight through Wednesday morning. Suppose that a very isolated total up to 3" in this vicinity can`t entirely be ruled out, especially given the late time of night and favorable cooler nocturnal temperatures. While some lingering snow will be possible in our far southeast through about noon on Wednesday, things should quickly clear out as the initiating shortwave/jet streak push east of the region. Guidance then once again develops a deeply-mixed PBL up to near 10 kft through the afternoon hours with very cold temperatures remaining in place aloft. Not seeing quite as much forcing upstairs to get things going like today with just general cyclonic speed shear overhead, but a developing lake breeze may provide enough surface convergence to squeeze out some additional snow/graupel showers with heating during the afternoon, mainly in the vicinity of the I-90 corridor counties. Wouldn`t expect any accumulation from this next bout of activity. Carlaw && .LONG TERM... 320 PM CDT Thursday through Tuesday... Things look pretty tranquil all things considered through the day on Thursday with temperature rebounding into the mid and possibly even upper 40s. We will be quickly turning our attention off to the south and west by Thursday evening as the next robust jet streak begins to develop across the Southern Great Plains which should begin to facilitate at least some degree of low-level cyclogenesis into Friday morning. Robust isentropic upglide/WAA really looks to get cranking more notably Thursday night and through Friday morning and with the greatest magnitudes generally off to the south of I-80, at least based on today`s multi-model consensus. Stout upper level divergence and the attendant thermally direction portion of the ageostrophic jet circulation looks to result in a low-level mass response that should encourage an increasingly robust f-gen circulation. This should encourage a SE-NE oriented band of developing moderate precipitation, with it looking increasingly likely to set up across parts of central Illinois and gradually shifting northward with time into Friday morning. The northernmost terminus of precipitation still remains in question, but guidance does now seem to be honing in on I-88 or the Illinois/Wisconsin state line. Any potential for heavier/steadier precipitation rates now may maximize across our I-80 and south counties with forecast QPF amounts supporting the potential for several inches of accumulating snowfall before things taper off/mix with and change to rain through Friday afternoon. The good news is that with the high sun angle, any snow that does fall should melt readily through afternoon and into Saturday. Temps will rebound heading into the weekend, but do look to remain near and just below normal for mid-April, although there is a potential for temperatures to overperform a bit on Saturday and have nudged highs just a wee bit above the blended guidance. At this time, conditions look dry from Friday night through Saturday as mid-level and surface ridging quickly crosses the region. Longwave troughing will re-establish over Hudson Bay later this weekend. An embedded trough axis and associated cold front swinging across the Great Lakes region late Saturday night and Sunday may bring with it chances for showers. Looking farther ahead, active split flow looks to continue which should keep a somewhat unsettled weather pattern going here into the middle and end of next week. Carlaw && .AVIATION... For the 00Z TAFs... Aviation forecast concerns: * Snow showers ending and winds diminishing early this evening. * Potential for a period of light snow early Wednesday morning, and additional scattered snow showers Wednesday afternoon. * Weak lake breeze Wednesday afternoon expect to affect KGYY. Lowering sun angle and loss of diurnal "heating" will allow scattered snow showers to dissipate early this evening, and gusty west winds to diminish. VFR ceilings should also scatter out with the loss of low-level instability. Attention then turns quickly to the west, where a mid-level disturbance was evident in satellite imagery across the KFSD region. This wave is expected to track eastward tonight, with a band of light snow developing from southern IA into northern IL after midnight. The primary axis of snowfall with this is expected to be across the I-80 corridor and just south, but with light snow extending as far north as the I-88 corridor across northern IL including KORD/KMDW roughly in the 08-12Z time frame. Visibility should be lower (potential IFR) at KGYY, and somewhat better (mainly MVFR) farther north toward KORD. KRFD may briefly get clipped after 07Z or so, but it looks like it will mainly be south of there. Snow should end early Wednesday morning, with VFR conditions thereafter. Deep mixing is expected to develop with diurnal warming again Wednesday afternoon, with scattered snow showers developing due to deep surface-based lapse rates beneath cold air aloft. Upper level support is a little weaker than today, so coverage and visibility impacts are expected to be less significant than today. The deep mixed layer should also support breezy west winds once again, though weaker than today. Various model guidance does indicate a lake breeze developing into KGYY with northeast winds in the afternoon, but not pushing inland into northeast IL as far as KORD and KMDW. Any scattered snow showers should again dissipate by sunset Wednesday, with winds also diminishing. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSChicago www.twitter.com/NWSChicago www.youtube.com/NWSChicago
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
930 PM EDT Tue Apr 14 2020 .SYNOPSIS... A cold front will move southeast through the region overnight, bringing a chance of showers along with colder temperatures. Chilly high pressure will then build across the region from the Midwest Wednesday and Thursday, as the front pushes well to our south. The front will retreat back northward into the Carolinas over the weekend, bringing a chance of rain as low pressure tracks eastward along the front. && .NEAR TERM /TONIGHT/... As of 930 PM Tuesday... Still on track for a light precip event overnight into early Wed morning, focused on the VA border areas and NE CWA. The latest surface analysis shows the frontal zone having pushed northwestward through eastern and southern sections of central NC since lunchtime, with a surface low now just WSW of CLT tracking slowly along the front to the NE. But the advancement of chilly/dense high pressure through the Mid Miss Valley across the Ohio Valley/KY into WV is tightening up the frontal zone to our NW and pushing it southeastward into W NC/SW VA, which has helped stall the NW push of the coastal front. Dewpoints have fallen at places like Blacksburg and Galax in VA and Boone and Asheville in NC, with a slight increase in speed and shift of winds to NW as the MSLP gradient has tightened in this region. The 00z GSO sounding shows fairly steep lapse rates (fueling a few electrical pulses within the precip band now NW of INT) and depicts today`s good heating and mixing, but the moisture is fairly shallow (5000-8500 ft deep) with high cloud bases and a fairly dry subcloud layer (surface dewpoint depression over 15F) that will be tough to overcome, suggesting small precip amounts. But with the approach of the front from the NW combined with the now-stationary frontal zone across S and E NC and ensuing increasing moist upglide, we should still see showers break out over the area, focused on areas near the VA border and in NE NC down into the central Coastal Plain overnight. Again, though, amounts will be limited by the relatively dry low levels, and of the CAMs, the 00z HRRR and 12z high-res WRF-ARW (which are doing the best currently) show well this more spotty coverage. Have taken pops down just slightly (by 5-10%) as it looks like our SW sections could stay totally dry, but this retains the higher pops across the far N and NE. Temps remain tricky with strengthening CAA overnight as the cold front drops SE through the area, bringing increasing and gusty NW winds drawn in by the departure of the surface low as it moves NE through eastern NC. Have made minor adjustments but stayed close to around 40 NW ranging to the upper 40s in the SE. -GIH Early afternoon satellite imagery and surface analysis reveals the presence of an elongated longwave trough over the lower OH valley, which is bringing light precip to the western Appalachian mtns as of 18Z. Meanwhile across NC, the boundary that moved through the area overnight and brought drier air into the area has started its retreat northward as a warm front. Widespread dewpoints in the 30s and 40s have since been replaced by upper 40s and lower 50s although some degree of drier air has remained in place across the Triad thus far. Similarly, temperatures have warmed into the mid 70s across the Sandhills behind the front. Cooler temps remain in place along the NC/VA border where WAA has been weak. Two focus areas for the rest of the evening/overnight hours. The front to the west will move across the Appalachians tonight, meanwhile a weak coastal low will develop off the SC coast. Weak ascent associated with both of these disturbances should be enough for light showers to develop across the entire area late this evening/overnight. Thunder chances are limited and probably too low to include in the forecast (MLCAPES only around 100-200 J/KG) but would be confined to the Sandhills/areas east of I-90 if it happens. Rainfall amounts should be on the light side with nearly all flavors of deterministic and probabilistic guidance suggesting 0.10-0.20 inches at most. Despite the cloud cover and precip in the area, temps will drop quite a but tonight as modest post-frontal cold advection should commence shortly after 06Z. Lows in the low to mid 40s is the consensus of all the better performing guidance. Winds could also be breezy at FROPA with BL mixing supported all night long and would not be surprised to see 10-15 mph winds through the pre-dawn hours. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 150 PM Tuesday... Skies will clear out on Wednesday as surface high pressure builds in from the north. Any lingering precip in the morning hours should quickly taper off before noon. It will be considerably cooler Wednesday into Wednesday night, best performing guidance is suggesting highs in the low to mid 50s. Lows Wednesday night could be problematic despite guidance values in the upper 30s/lower 40s. Idealized scenario of clear skies/light winds could result in patchy areas of frost. May need to go with a Frost Advisory Wednesday night once we can pin down the coldest areas. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 256 PM Tuesday... A +1025 mb surface high centered over the lower Ohio Valley will build east across the southern Mid-Atlantic states through Thursday night, before shifting offshore on Friday. This high pressure will result in a continuation of seasonably cool, below-normal temps through Thursday night, with some patchy frost possible across the norther Piedmont counties Friday morning. Weak southerly return flow will allow temps to moderate to near normal to end the work week. A shortwave trough ejecting east from the Central Plains through the Ohio Valley on Friday will reach the Mid-Atlantic region late Friday night and Saturday. This system will drag a cold front into the area Friday night with the front forecast to slowly push south through the area on Saturday. Showers are expected with the the front, although convective coverage and QPF amounts are in question due to model differences with the strength of the upper trough. This front is forecast to briefly stall just south of the area late Saturday, before returning north as a warm front on Sunday. CAD conditions are likely to develop over the NC Piedmont as the arrival of shortwave impulses embedded within the low-amplitude, zonal flow aloft will lead to overrunning lift and precip Sunday and Sunday night. Additionally, we will need to closely monitor the threat for some stronger convection and destabilization across eastern/southern portions of the area, given that a decent amount of the NWP guidance indicates some weak low pressure wave development along the warm front(s). Drier, more tranquil conditions are expected to return early next week. && .AVIATION /00z WEDNESDAY THROUGH SUNDAY/... As of 915 PM Tuesday... VFR conditions currently persist across the entire area, with just some scattered mid-level clouds around 5-7 kft. A cold front currently just west of the Triad will make its way east across central NC over the next several hours. At the same time, a weak low pressure system currently over South Carolina will move east off the Southeast US coast. These two features will result in some light showers across parts of the area late tonight through tomorrow morning. The best chance for this is at the eastern TAF sites (RDU/FAY/RWI), closer to the surface low and where forecast soundings indicate a deeper moisture layer. In addition, as the front moves through the area, winds will shift to a northerly direction and become gusty, reaching 10-20 kts. Clouds will also begin to thicken. At this time keep only low VFR ceilings at INT/GSO as upstream sites are generally staying VFR, and the moisture layer is forecast to remain shallow. Farther east at the remaining TAF sites, ceilings should drop to MVFR after midnight, with a slight chance for IFR ceilings at FAY/RWI, but confidence of the latter is low so have kept it out of the TAFs for now. By late morning, showers will move out of the area and ceilings will improve to VFR. Drying behind the front should allow for clear skies by the afternoon. Looking beyond 00z Thursday: VFR conditions will continue across the region for Thursday and Friday as high pressure builds in. Then forecast confidence becomes lower as an unsettled pattern returns. An upper trough and cold front will move through the area Friday night into Saturday, bringing more showers and sub-VFR conditions. Additional disturbances could bring sub-VFR conditions to the area on Sunday and Sunday night as well. && .RAH WATCHES/WARNINGS/ADVISORIES... None. $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/Leins SHORT TERM...Leins LONG TERM...CBL AVIATION...Danco