Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/31/22

See below for an aviation forecast discussion for the 00Z TAFs.

&& .SHORT TERM...(This Evening through Saturday Night) Issued at 235 PM CST Fri Dec 30 2022 A broadly progressive mid level flow pattern will continue for the short range. A couple of weak waves are forecast to move through the flow, but overall moisture looks pretty scant and really am having trouble seeing any measurable pcpn through the period. The main issue this weekend may well be areas of fog overnight and early in the day due to relatively weak winds and plenty of snow cover to enhance low level moisture. Tough to say exactly where to put fog so will rely on models to some degree. In this persistent low level pattern will stick with and not stray too far from NBM temps, which is to stay near seasonal norms. .LONG TERM...(Sunday through Friday) Issued at 235 PM CST Fri Dec 30 2022 Really, not a lot to add to the extended discussion that hasn`t already been hashed out of the last 3-4 days. Deterministic guidance remains in its own camps, with the GFS having the more northerly track (though this has shifted south slightly) and the EC the more southerly track and the Canadian leaning towards the EC. Ensembles follow the trends of the deterministic guidance, with fewer EC members bringing moisture into the CWA compared to this time yesterday. While the GFS is the more northerly track, profiles for KABR/KATY show less of a warm layer influence on p-type, with any freezing precipitation generation being the response to a lack of ice in the dendritic growth zone. As such, NBM 4.0 has lowered probabilities for mixed precip, and even GEFS ensembles have trended towards almost exclusively snow (though Watertown still has a small probability for ice). The caveat to this is the NBM 4.1 which has some not- insignificant ice probabilities to our south. Will stick with blended guidance (NBM 4.0) which maintains mainly snow as the p- type. As for snow totals, confidence is low, GEFS plumes are still all over the place, and the NBM 4.0 and NBM 4.1 show significant differences in mean snowfall potential. Confidence in winds is also low, with placement of surface highs nearly over the CWA in the EC and a gradient across the state in the GFS. Peak sustained wind in NBM 4.1 is only 20kts for our more favored locations, and at these temperatures blowing snow model would require over a 1/2" per hour rate to get reduced visibility to even consider blowing snow impacts. Since that is the worst case and most of forecast areas NBM 4.1 winds are sustained at 10 to 15kts, at this point will not include any mention of blowing snow. && .AVIATION...(For the 00Z TAFS through 00Z Saturday Evening) Issued at 600 PM CST Fri Dec 30 2022 Terminals KABR,KATY,KPIR,KMBG Low clouds and fog across northeast South Dakota (KABR/KATY) and west central Minnesota are expected to fill in and spread west toward the KPIR/KMBG terminals over central and north central South Dakota overnight. Expect LIFR, or perhaps even VLIFR, at times in dense fog and very low stratus. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...Dense Fog Advisory until 6 AM CST /5 AM MST/ Saturday for SDZ003>011-016-017-021-036-037. MN...None. && $$ UPDATE...Dorn SHORT TERM...TDK LONG TERM...Connelly AVIATION...Dorn
National Weather Service Wakefield VA
837 PM EST Fri Dec 30 2022 .SYNOPSIS... A storm system and associated weak cold front moves across the area for New Years Eve, bringing the next chance for rain. Drying out and remaining warm Sunday through early next week. Rain chances increase once again by the middle of next week with a second, stronger cold front approaching the region. && .NEAR TERM /THROUGH SATURDAY/... As of 835 PM EST Friday... Latest analysis reveals an inverted/coastal trough along/just offshore of the coastal Carolinas this evening. To the west, a weak cold front extends from western QC/ON into the lower and middle MS Valley, with a secondary weak sfc low lifting along the front over the Tennessee valley. Forecast is in good shape at this hour. Clouds have increased as expected this evening, and will continue to thicken and lower overnight. Light isentropic overrunning along the coastal trough will bring some light showers to coastal NE NC and southside hampton Roads after midnight. A second area of weak shallow lift will result in some sprinkles or very light rain over the VA piedmont mainly south of US-460 late tonight, but otherwise expect inland areas to remain dry tonight. WAA will also allow for fog to develop late, mainly along and just west of the encroaching coastal front, as it lifts N along the coastal plain into Saturday morning. Patchy fog will be possible farther inland to the west of I-95, but expect widespread fog to develop late tonight, and quite possibly becoming dense in spots along the SE coast per HRRR and NARRE trends. Not confident enough to get into any fog headlines at this stage, but could very well need them along the coast overnight. Lows tonight into the 40s. Fog lingers through the morning Saturday before beginning to lift by late morning- early afternoon, as more widespread rain moves into the piedmont, and winds become S/increase to 5-10 mph. A main area of low pressure moves through the Ohio Valley and into the interior Northeast Saturday, as the secondary low lifts across the mid-south, reaching, then crossing the local area through Sat night. Both lows eventually phase Sat night over the Northeast, which shunts a cold front through the area. Made some minor modifications to PoP timing with the evening update. First batch of light overrunning showers lift along the coastal front over the coastal plain late tonight, while some spotty light showers or sprinkles lift across the piedmont. As the main slug of isentropic upglide/overrunning moisture arrives and lifts across the area ahead of the approaching upper trough tomorrow afternoon and evening, pushed likely to categorical PoPs across the region from NW to SE from late Saturday morning through Saturday night. A few rumbles of thunder cannot be ruled out across far E/SE portions of the FA by Sat evening, as the secondary low drags a warm front and some weak (mainly elevated) instability into the area. However, a weak in-situ wedge should keep much of any modest instability confined to our south. Any showers taper off from SW to NE by around midnight. Overall, numerical guidance continues to lower total QPF, which now stands ~0.3-0.7" (highest across the SE half of the area). Some locally higher amounts are possible, again mainly across the SE one-third of the area. Highs Sat in the upper 50s NW to upper 60s SE. Clouds begin to clear just as we ring in 2023 Sat night into Sunday morning, with expected overnight lows in the mid 40s NW to lower 50s SE. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 255 PM EST Friday... High pressure remains centered offshore through mid-week. Dry weather returns New Year`s Day with mostly sunny to partly cloudy skies. Given sunshine, W downsloping winds, and any cool air lagging behind the weak cold front, expect highs to be above guidance on New Year`s Day in the mid 60s N to upper 60s to near 70F S. Mostly sunny early Mon with cirrus moving in from W to E during the afternoon. Again, went above guidance for Mon given SW winds and sunshine as well as thickness values supporting warmer temps. Highs Mon in the mid 60s NE to upper 60s to around 70F SW. Lows in the upper 30s to lower 40s Sun night and mid 40s (lower 40s over the Eastern Shore) Mon night due to clouds increasing overnight. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 255 PM EST Friday... The ridge amplifies over the East Coast Tues before shifting offshore late Tues through Thurs. This will result in above normal temps continuing through mid-week. Low pressure tracks well NW of the area through the W Midwest Tues. The trailing cold front will be slow to cross the area with at least one more low likely forming along the front from mid-late week. However, confidence on location and timing of the secondary low remains low. Nevertheless, PoPs look to increase Tues evening, continuing through early Thurs, with the best chance of showers Wed (likely PoPs). Given days of WAA, dewpoints rise into the lower 60s Wed which may allow for some storms to develop. However, given that this will be early Jan and confidence in the position and track of any secondary low remains low, will hold off for now in adding thunder to the forecast. The cold front pushes through Wed night with a return to near normal temps by late week. Highs in the upper 60s to near 70F Tues, upper 60s to lower 70s Wed, mid 50s NW to lower to mid 60s SE Thurs, and mid to upper 40s NW to lower to mid 50s SE Fri. Lows in the mid to upper 50s (perhaps 60F in spots) Tues night, mid 40s NW to lower 50s SE Wed night, lower to mid 30s NW to lower 40s SE Thurs night, and mid to upper 20s NW to lower to mid 30s SE Fri night. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... As of 705 PM EST Friday... VFR conditions across area terminals early this evening will give way to gradually deteriorating flying conditions through the night, with poor flying conditions expected on Saturday. Increasing clouds this evening tonight, particularly after midnight, with CIGs remaining mainly VFR until around midnight for most terminals, except for MVFR and some spotty showers developing along the immediate coast). After 06z/1 AM EST, expect IFR/LIFR CIGs to develop E VA/NE NC along an encroaching coastal front, with lowering CIGs spreading farther inland by sunrise. There will likely be 1-2 hours of MVFR CIGs between the VFR and IFR/LIFR transition. Fog will also develop after midnight, initially near the coast, with fog also spreading inland into Sat morning. Some patchy drizzle/light rain possible across the piedmont overnight, but otherwise remaining mostly dry tonight. Lowest VIS/CIGs look to be along and E of the I-95 corridor where areas of fog appear likely, with guidance trending toward dense fog likely developing along the coastal terminals after 08-10z. VIS and CIGs look to drop into LIFR (LCL VLIFR) late tonight through mid- morning Saturday. As rain moves in from the west, expect fog will diminish a bit by late morning/early afternoon inland and from mid to late aftn along the coast. However, expect CIGs to remain in IFR/LIFR range through the day. Winds remain light and variable (or calm) overnight, and become S 5-7 kt by Sat afternoon. Outlook: IFR/LIFR conditions continue through early Sunday morning as a cold front crosses the region. VFR conditions look to return through Sunday morning. VFR conditions then persist through the middle of next week, as high pressure rebuilds over the mid-Atlantic from the W-SW. && .MARINE... As of 255 PM EST Friday... Upper air analysis shows a trough over the central CONUS and a strong ridge off the SE coast. Surface high pressure, centered just offshore this afternoon, will slowly translate eastward tonight as weak surface low pressure along the Gulf Coast begins to lift NE. Local winds are generally S 5-10 kt, with southern waters showing more of an easterly component. Waves are 1 foot or less with seas 2- 3 ft. The surface low is forecast to move into the Ohio Valley by Saturday morning and into western NY by the evening, bringing a cold front across the area overnight. Warm advection over the cooler waters will bring the chance for marine fog tonight into Saturday. Southerly flow increases to 10-15 kt by late Sat afternoon and averages ~15 kt in the rivers, bay, and sound with 15-20 kt offshore from the evening into the overnight ahead of the front. Winds become W ~15 kt behind the boundary but models continue to show little in the way of cold advection and only marginal chances for winds above SCA thresholds. Seas are forecast to increase to 3- 4 ft on Saturday with guidance continuing to show the potential for seas to build to 4-5 ft well offshore. Waves increase to 2-3 ft Saturday night before falling back to 1-2 ft by Sunday. Will hold off on any SCA headlines for the Atlantic waters with this forecast given the tendency for wave guidance to over perform reality in SW flow events. High pressure builds in behind the front with generally tranquil weather expected through Tuesday before another system impacts the region mid to late week. West winds will gradually diminish to 10-15 kt by late Sun aftn-Sun evening, and become SW 5-10 kt Sun night. Seas will subside to 2-3 ft by Sun night. Sub-SCA conditions are expected on Mon/Tue. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...RMM NEAR TERM...MAM/RMM SHORT TERM...RMM LONG TERM...RMM AVIATION...MAM/RMM MARINE...RHR
National Weather Service Bismarck ND
938 PM CST Fri Dec 30 2022 .UPDATE... Issued at 936 PM CST Fri Dec 30 2022 Stratus and areas of fog continue to expand across much of central and eastern North Dakota this evening, as well as portions of western ND. Adjusted the forecast based on latest imagery and trends. Thus far will hold off on any fog headlines with observed visibility greater than 1-2 miles and web cam imagery not indicated a need yet. Will continue to monitor. UPDATE Issued at 548 PM CST Fri Dec 30 2022 Main forecast challenge tonight will be low stratus and fog expanding across much of the area, lingering central and east Saturday morning and possibly into the afternoon some areas. Utilized a blend of the HRRR and NBM 4.1. Will definitely be making adjustments to sky cover and fog coverage through this shift this evening based on observations and trends. && .SHORT TERM...(This Evening through Saturday) Issued at 213 PM CST Fri Dec 30 2022 Relatively weak zonal flow persisted aloft, which will aid in returning stratus and fog tonight across much of the state. Southerly flow at the surface continues ahead of a weak low that will cross the state tomorrow, bringing a slight chance of light snow across areas near the International Border. This afternoon, stratus had eroded over most of western and central North Dakota, lingering in the far north and the James River Valley. Patches of stratus are still present in south central North Dakota where the dew point depression remains fairly small. It looks likely that stratus and fog will again develop as temperatures cool later this evening. High-res guidance has been bullish on developing stratus as early as late this afternoon, however this may be a bit early and widespread development should wait until what little boundary layer mixing exists diminishes with loss of insolation. Tomorrow, cloud cover and fog should be focused mainly central to east as the surface low should clear out the west. Added a slight chance of light snow along the low over far northern North Dakota, but any accumulations should be very light. .LONG TERM...(Saturday Night through Friday) Issued at 213 PM CST Fri Dec 30 2022 There is a chance of accumulating snow in southeast North Dakota Monday and Tuesday, but the probability of heavy snow remains below 30%. Cool high pressure will be in place on Sunday in the wake of the previous shortwave. Afternoon forecast highs range from 15 to 25. A deep trough will dig out of the Four Corners region with a shortwave and surface low moving out of Colorado on Monday. The track of this Colorado Low has been somewhat questionable this past week, but seems to be converging on a southward track, influenced by a northern stream shortwave which should phase with the Colorado wave and ultimately keep it south of most of North Dakota. Southeast North Dakota remains under modestly higher probabilities from recent ensemble runs to receive accumulating snow, with LaMoure, Dickey, Logan, McIntosh in the 15-25% range to see greater than 6 inches. There isn`t a large drop off in probabilities from 2 or 4 inches up to at least 6 or 8 inches, which speaks to the likelihood of a strong northwest gradient in snowfall accumulation, where areas may see heavy snow or nearly nothing, and the probability of something in between is low. While low visibilities with blowing snow would be a concern if this northern track does produce snow in southeast North Dakota, the fact that most guidance keeps snow south of the South Dakota border (and therefore the greater pressure gradient), the conditional probability of blowing snow looks low at this time. The forecast behind this system is dry for now with northwest flow possibly leading to some ridging takes hold. Cool temperatures prevail under this flow as well, with CIPS analogs favoring below normal temperatures through the middle of next week. && .AVIATION...(For the 00Z TAFS through 00Z Saturday Evening) Issued at 548 PM CST Fri Dec 30 2022 IFR to LIFR conditions in stratus and fog will quickly redevelopment this evening over central and eastern terminals of KJMS, KMOT, and KBIS. KDIK will also see a period of MVFR to IFR stratus this evening before conditions improve there overnight as winds become more westerly. KXWA should remain VFR. Conditions will improve for KMOT and KBIS after 15Z Sat morning, and for KJMS after 18Z Sat afternoon. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...NH SHORT TERM...AE LONG TERM...AE AVIATION...NH
Area Forecast Discussion
National Weather Service Grand Forks ND
958 PM CST Fri Dec 30 2022 .UPDATE... Issued at 955 PM CST Fri Dec 30 2022 Fog is the main issue overnight into Saturday morning. After initially seeing some spots in the 1/2 to 1/4SM range in fog near 00z, there has been a slight increase in south-southeast winds into the 10-20 kt range in E ND, where HRRR and NBM suggested the best chance for low vsbys overnight. Lowering vsbys in fog certainly still possible overnight but less clear if we will get into dense fog range. Areas of fog covers much of the fcst area and will leave as is. Temps not dropping much overnight. UPDATE Issued at 602 PM CST Fri Dec 30 2022 Per NBM and consort vsby forecasts tonight it will be a foggy one for many areas with potential for dense fog with highest percent chance west of the Red River. Considerable low level moisture stuck in the boundary layer with a light south wind. Areas that did clear out a bit this afternoon (DVL and PKD) will cool down to the dew pt and likey fog in too. Expanded fog mention to inclue most of the forecast area into Saturday morning. && .SHORT TERM...(This evening through Sunday night) Issued at 127 PM CST Fri Dec 30 2022 Key Messages: 1.) Mostly quiet weather will continue for the short term period. 2.) Snow and freezing drizzle are possible at times through Sunday night. Widespread impacts are not anticipated at this time. Discussion... The surface pattern is dominated by a weak pressure gradient over our area, contributing to weak southerly winds this afternoon. A thick stratus deck continues to linger around the area. Within this stratus, areas of flurries are possible however impacts will remain minimal. For Saturday, a weak shortwave-clipper will progress through the region. Dry midlevels should inhibit precipitation impacts. At the moment, the greatest chance for snow is closer to the international border, especially around the Turtle Mountains. Sunday will feature more of the same of the recent pattern. Mild temperatures with little to no accumulating snow/rain. The pattern does begin to shift as we approach the long term period as we shift to southwest flow. .LONG TERM...(Monday through Friday) Issued at 127 PM CST Fri Dec 30 2022 Primary focus continues to be on the track/evolution of the system early next week and any potential for winter travel impacts. Regarding the system Monday into Tuesday: Trends have started to favor a southern track placing the highest probability for warning impacts south of our CWA (though there is still 10-20% chance based on combined ensembles in our far southern CWA). The probability for 3" or greater snowfall is also south of our CWA based on the ECMWF ensemble, but GEFS still maintains probs for 3"+ in the 30-50% range along and south of the I-94 corridor in our CWA. This southern shift in NBM reflects the ECWMF ensemble tends and makes sense considering the larger scale/progressive mid level flow across the CONUS and less amplified ridging to the east. As the pattern is set up a stronger system farther north needs more amplified ridging ahead of it to slow it down and turn north. Ultimately we still have some potential for winter impacts within our area (particularly in our south), and I don`t want to completely discount the possibility for additional shifts in track or even mesoscale forcing on a smaller scale that could still lead to localized warning impacts. A lot can still change at this range. Progressive mid level flow continues through the long range with shortwave ridging followed by westerly zonal/split-flow by the end of next week. No impactful weather is anticipated through the rest of the long range periods and NBM favors dry conditions/no measurable snowfall. While a few days may feature highs in the single digits/lower teens this is still not outside of what could be considered "seasonal", and any nights that clear out have potential for lows in the negative temperatures in the single digits mid to late next week (again not outside of seasonal ranges). Colder arctic air will remain bottled up in northern Canada and without an amplification of the mid level pattern we are not likely to see deeper cold arrive during the next 7 days. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 602 PM CST Fri Dec 30 2022 Poor flying conditions into Saturday either due to IFR ceilings and/or IFR vsbys in fog, potential for LIFR. Improvement may be slow on Saturday. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...Riddle SHORT TERM...Perroux LONG TERM...DJR AVIATION...Riddle
National Weather Service Hastings NE
459 PM CST Fri Dec 30 2022 ...AVIATION UPDATE... .DISCUSSION...(This evening through Friday) Issued at 248 PM CST Fri Dec 30 2022 Key Messages: * Nice weekend with above normal highs in the 40s south central Nebraska to near 50 over north central Kansas. * Big Monday into Tuesday storm system, but plenty of uncertainty regarding storm track. At this time the heaviest snow appears to be north of our area, perhaps more of a freezing rain event for much of our area (possibly a pretty impactful freezing rain event). * Colder for several days next week on the back side of this storm system. Weekend... There will be zonal flow across the middle of the country and then a bit of upper ridging as the next upper trough digs over the west coast. This will make for a warmer than normal weekend. Any remaining snow cover should melt except for some of the bigger piles and drifts. Monday into Tuesday Winter Storm System... The same model trends from the past few days continue. The GFS and GEFS continue to be the furthest northwest with the 500 mb upper low track, the 12/30 12Z GFS taking the upper low from northeast Colorado towards Valentine, NE. On the other hand, you have the 12/30 12Z ECMWF that takes the 500 mb upper low more easterly out of Colorado on a track along the NE/KS state line towards Nebraska City, thus giving our forecast area much more wintry precipitation, especially freezing rain. The Canadian model falls somewhere in between. A long look at the 50 ECMWF ensemble members indicate that the ECMWF deterministic run is more in line with the furthest southeast cluster of ensemble storm tracks, while over half of the overall ECMWF ensemble storm tracks are further northwest. Consequently, with only the southern most ensemble members getting heavy snow down into the heart of our forecast area, it is currently more likely that the heavy snow will be north of our area and thus freezing rain may be our biggest concern with this system. It`s still far enough out that things could shift south towards the more southern model solutions, which could give us an impressive and memorable winter storm event of both ice and snow. However, at this time at least some ice issues are the primary concern with the snow probably being more of an issue across our far northern zones and points north from there. Keep up to date with the latest forecast and hopefully we will start having more certainty regarding the storm track by this weekend. The storm will likely last into Tuesday, which will be colder on the back side of this system. There does appear to be wind with this winter storm, but not as much wind as we have had with some of our recent storms, probably more in the 20 mph gusting 30 mph range. However, this is more than enough wind to cause problems if we do end up getting an icing event. Wednesday and Thursday... We should be colder and likely below freezing for highs for anywhere that has fresh snow cover, but we are not going back into the deep freeze with this one. Friday... We should moderate fairly quickly as an upper level ridge moves in pushing highs back above freezing. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday) Issued at 445 PM CST Fri Dec 30 2022 The forecast challenge for tonight will be if the area sees and BR from the melting snow today. The NAM is the most aggressive and saturates the SFC. The HRRR SFC vis product is only show 6 to 8sm in BR. The RAP and GFS hint at some moisture at the SFC, so will go with 6SM BR for now. Forecast mid-level ceilings tonight along with SFC winds becoming more southwesterly should keep FG at bay. A weak LLJ will be over the area tonight which will cause some sheer, but not enough to put a LLWS remark in the TAFs. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ DISCUSSION...Wesely AVIATION...Beda
Area Forecast Discussion
National Weather Service Lincoln IL
815 PM CST Fri Dec 30 2022 .SYNOPSIS... Issued at 311 PM CST Fri Dec 30 2022 Rain east of I-57 will gradually come to an end Friday night, while dry conditions will continue west. Aside from a slight chance of showers Saturday evening with a weak warm front, dry weather is forecast to continue through at least Monday morning when the next system approaches from the southwest. && .UPDATE... Issued at 813 PM CST Fri Dec 30 2022 Light to moderate showers continue roughly along and east of a Pana to Rantoul line this evening and will persist several more hours. Precip should exit the state by around midnight. Meanwhile, surface high is centered near Quincy this hour and will gradually spread east across central Illinois overnight. At least patchy fog development remains a concern within the weak winds and humid boundary layer conditions, though guidance has been backing off on the fog threat some. Latest NBM shows probs of visibility less than a mile generally at 20-30 percent or less across the forecast area. && .SHORT TERM...(This evening through Saturday) ISSUED AT 311 PM CST Fri Dec 30 2022 DESI`s cluster analysis suggests good agreement in the upper level synoptic pattern in the short term, with only two 500hPa height clusters for days 1 and 2 each showing a continuation of SW flow across the MS Valley ahead of a negatively tilted trough meandering gradually east. The moisture axis which mid level water vapor imagery suggested stretched northward into IL from the Gulf of Mexico is projected to finally exit our area, bringing an end to the precipitation in our SE counties, late tonight. However, a weak perturbation diving southeast along the back of the upper trough could spark a couple showers Saturday afternoon before dryer air filters in from the west. The CAMs depicting simulated reflectivities across our west have these showers mainly west of I-55 - in areas that will have theoretically received little rain from our current weather maker. Behind these showers, temperatures are forecast to climb tomorrow afternoon/evening as warm air advection begins to gradually overspread the Midwest well in advance of the next storm system taking shape to our west. Though it`ll be cool tomorrow relative to our past couple days of warm weather, our highs are forecast to be in the mid to upper 40s which is around 10-12 degrees above climatological normal; for reference, the average high on December 31st is 35F in Lincoln. Both high and low temperatures tomorrow will be a challenge, though, as cloud cover remains a source of uncertainty. With some rain continuing in our far southeast counties overnight, cloud cover should inhibit surface cooling for radiation fog, though saturation of the column by falling rain could be sufficient for patches of reduced visibilities, especially early in the night; further west where low cloud cover is more limited, radiational cooling could bring temperatures down to the dewpoint and result in fog, depending on whether winds become light enough. Largely due to the NAMNest and HRRR which bring visibilities down to less than a quarter mile in spots, HREF guidance forecasts a gradient in probabilities for sub 1 mile (1/4 mile) visibilities from 50% (40%) in our E to around 20% (10%) in our W CWA for early tomorrow morning. Depending on whether this fog materializes and how long it takes to burn off, especially east of I-55 where a greater depth of the column could be saturated, temperatures may cool less and warm less than forecast tonight and tomorrow. .LONG TERM...(Sunday through Friday) ISSUED AT 311 PM CST Fri Dec 30 2022 Main concerns during the extended forecast period are: 1. Flooding Potential 2. Severe Potential Deterministic models and their ensembles remain in general agreement in the upper pattern through the weekend, with uncertainty becoming more apparent by Monday, when a couple distinct scenarios become plausible as a storm system evolves across the Great Plains. Zonal 500hPa flow across the Midwest is forecast to come to an end by this time, as each cluster solution suggests amplification of the Rossby Wave with ridging east of the Plains and a trough somewhere between the Great Basin and Western/High Plains. The differences between the clusters is primarily driven by timing of the trough`s eastward progression, with the EPS driving the slower solution and the Canadian and GFS ensembles dominating the faster scenario. Thereafter, uncertainty in what happens with the upper large-scale pattern and hence any surface weather-makers increases, with the European ensemble generally tending towards a more quickly weakening trough over the Midwest/Great Lakes. Surface cyclogenesis appears likely on Monday, but where and how quickly it occurs will be a function of the upper trough`s strength and location. The deterministic CMC and GFS, which each are near the center of the cluster phase space and hence represent fairly well the mean of the grand ensemble for at least the upper level pattern for Monday and Tuesday, each have a surface cyclone forming beneath a 500mb vort max ejecting northeastward out of the Plains into the Midwest Monday evening. The ECMWF and GFS have this low tracking through eastern IA, while the CMC has it crossing central/western IL. Ultimately, the exact track will matter a whole lot for both rain amounts and potential for strong thunderstorms, along with temperatures. 1. Our first concern with this system will be flooding potential. A potentially robust LLJ developing ahead of the surface cyclone is expected to advect an impressive low level moisture plume into the MS and Ohio Valleys from the Gulf of Mexico, with the mean of the EPS suggesting PWATs around 300% of normal by Monday evening. In fact, southeast IL will have around a 60-70% chance for PWATs greater than 1.50" (the record for Jan 2 in Lincoln is 1.05"). Both the GFS and CMC have a swath of 2" or more of precipitation falling in a single 6 hour period Monday evening, though they disagree on where this will occur which is probably the reason that NBM has a broad area of probabilities from 15-25% for greater than 2" of rain across central IL. FFG is around 2.25" in 6 hours or 1.75" in 3 hours, so how quickly this rain falls will bear watching, especially given some of the frost depths measured this morning; theoretically, the warm weather between now and the time of heaviest rain will completely thaw the ground across the board, but if it doesn`t then even non-urban surfaces may act hydrophobically and flooding could be a bigger threat than it currently appears. 2. Severe potential for this system is not looking overly impressive, though still a lot of uncertainty exists. The grand ensemble (GE) mean suggests 100 to 150 J/kg of SBCAPE overspreading central IL Monday afternoon and evening, while the 90th percentile has close to 400 J/kg in our far south CWA. The GFS has around 50 kt of 0-6 km shear over Lincoln during the same time frame, which should be sufficient for sustained convective activity. However, the location and strength of the surface low will largely govern how much shear (and instability) our area experiences, and given instability is looking lackluster we`ll need to have quite a bit of shear to overcome that for organized thunderstorms capable of generating severe weather. The SPC has kept the northern extent of their day 4 convective outlook just south of our area, clipping just the far southern tip of the state, and with this we agree. As model agreement increases and details in the evolution of this system become apparent with time, we`ll have more to discuss in regard to severe potential. Otherwise it`ll likely be breezy Monday going into Tuesday as surface pressure gradients tighten with the passage of the low to our northwest. The GFS and EPS ensembles have peak 6 hour wind gusts increasing to 35+mph during this time period, so south/southwest gusts to 40 mph (outside of thunderstorms) appear a distinct possibility Monday night and/or Tuesday. Behind the front, which is projected to cross the region Tuesday or Tuesday night, cold air advection will bring an abrupt end to the 25+ degree above normal temperatures we`ll have to start the work week with overnight lows Wednesday morning expected to drop into the low 30s and perhaps even the 20s west of the IL River. By Wednesday afternoon, 75% of the GE have 850mb temperatures less than -4C. Additionally, a number of ensemble members have sufficient low level moisture that should enough sunshine occur for steep lapse rates off the surface, parts of the area could see snow showers on Wednesday and perhaps even on Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 521 PM CST Fri Dec 30 2022 Showers continue across portions of east central Illinois this evening but should taper off by late this evening. High pressure will build in from the west overnight allowing light northwest winds to become light and variable. Fog and low stratus will then develop overnight. Fog is expected to be thickest where the rain is currently occurring. Winds will set up out of the SE Saturday and expect conditions to improve back to VFR by late morning. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Deubelbeiss SYNOPSIS...Bumgardner SHORT TERM...Bumgardner LONG TERM...Bumgardner AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service San Diego CA
230 PM PST Fri Dec 30 2022 .SYNOPSIS... A strong cold front moving down the West Coast tonight will bring increasing chances for rain over and west of the mountains Saturday afternoon. Strong winds and heavy rain will move across the region Saturday night when road flooding is most likely. A Flood Watch is in effect for all coastal, valley and mountain zones Saturday night. Gale Warnings were issued for the Coastal Waters. Next week will remain active as a series of Pacific disturbances make landfall on the West Coast. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... *** Flood Watch issued from 6 PM Saturday to 2 AM Sunday *** Details below. A deep cloud layer blanketed most coastal, valley and mountain areas below 5,500 feet this afternoon. In contrast, the higher mountains and the deserts were sunny. The band of rain and mountain snow over northern CA this morning crept a little farther south this afternoon. At 2 PM the southern edge of the precipitation band had reached Lake Tahoe. The rain band and the associated AR will trek southward tonight and Saturday, crossing Southern California Saturday night. The timing and intensity of this cold front hasn`t changed. The rain here in SoCal will start to increase in coverage midday Saturday, mostly in Orange and San Bernardino Counties. The highest rain amounts on Saturday will be on the south and southwest facing mountain slopes of the San Bernardino County mountains where strong southerly 850 mb winds of 20-30 kt will produce orographic rain amounts of a 1/2" from the LA County line eastward to Crestline. This includes Lytle Creek and I-15 in the Cajon Pass. Rain shadowed areas of the Inland Empire will not see much if any rainfall on Saturday, anywhere from a trace to a few hundredths of an inch. The same goes for southern San Diego County near the Mexican Border, and all desert areas Saturday. The AR then moves across SoCal Saturday evening. It will move across SBD and ORA counties in the evening, and then across Riverside and San Diego Counties through midnight with a core IVT of 400-700 kg/m/s. The HRRR and WRF model rain rates in the San Bernardino and Santa Ana Mountains of 0.50"-0.80"/hr are most likely between 7 PM and Midnight Saturday. A Flood Watch has been issued for all coastal, valley and mountain areas from 6 PM Saturday to 2 AM Sunday. This is when road flooding and mud/debris flows will be most likely. HRRR and WRF rain totals of 2-4" are projected on the south and southwest facing slopes of the San Bernardino Mountains. Elsewhere the southwest facing slopes in San Diego, Orange and Riverside Counties should see 1.5-3 inches. Coastal and valley areas will see 0.75-1.5 inches. The high deserts around 0.50" and the lower deserts from 0.25-0.50 inches. This will be a warm storm with snow levels above 7,500 feet so most of the precip will fall as rain. Snow impacts will mostly be confined to areas above 8,000 feet where several inches will accumulate. Snow levels fall to 6,000 feet late Saturday night with the passage of the cold front, but by then the heaviest precipitation will have moved east. The San Diego River at Fashion Valley is forecast to reach 7.8 feet, high enough for water to flow over the low water crossings at Fashion Valley Road, Avendia Del Rio and Camino De La Reina. A High Wind Watch is in effect for the San Bernardino Mountains and High Deserts from 10 AM to 10 PM Saturday. The storm will move quickly east Sunday morning followed by a brief period of dry weather into early Monday. Another shortwave in the Pacific jet will bring rain chances back into SoCal Monday night and Tuesday. This is a weaker system, but still has plenty of moisture for another round of widespread rain and mountain snowfall. A lower snow level (5000-5500 ft.) should result in few inches of snow below 7,000 feet. There are more perturbations in the strong zonal jet crossing the Pacific later next week, so rain and snow chances remain in the forecast through next Friday. $$ .AVIATION... 302130Z...Coast/Valleys/Mountains...Widespread BKN/OVC clouds will continue through Sat with variable bases 1500-3500 ft MSL and areas of terrain obscurations layered at times to 25000+ feet MSL. Local VIS 2-4 miles will occur due to ISOLD -SHRA and BR below the clouds. South/southwest winds 15-25 kt with gusts 30-40 kt will develop in the San Bernardino County Mountains after 17Z Sat and spread to the Riverside County and San Diego County Mountains after 20Z Sat. Deserts...SCT-BKN clouds at/above 10000 feet MSL will continue through Sat with unrestricted VIS. && .MARINE... A storm system from the northwest will bring strong winds and hazardous seas Saturday evening through Sunday evening. Northwest winds of 20 to 30 kt with gusts 35 to 40 kt are expected over the waters. A Gale Warning has been posted for the outer and inner waters. Combined seas of 10-15 feet are likely Sunday, highest in the outer waters, with the dominant periods 8-10 seconds. && .BEACHES... A west-northwest swell of 10-15 feet from 280-290 degrees at 8-10 seconds will produce high surf at the beaches Sunday through Monday, with 5 to 8 feet in Orange County and 6-9 feet in San Diego County. A High Surf Advisory is in effect Sunday through Monday. The relatively short period of the swell will be the limiting factor despite high seas in the coastal waters. Surf will gradually diminish Monday. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Flood Watch from Saturday evening through late Saturday night for Orange County Coastal Areas-Orange County Inland Areas- Riverside County Mountains-San Bernardino County Mountains- San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Mountains-San Diego County Valleys-Santa Ana Mountains and Foothills. High Surf Advisory from 4 AM Sunday to 6 PM PST Monday for Orange County Coastal Areas-San Diego County Coastal Areas. High Wind Watch from Saturday morning through Saturday evening for Apple and Lucerne Valleys-San Bernardino County Mountains. PZ...Gale Warning from 8 PM Saturday to 8 PM PST Sunday for Coastal Waters from San Mateo Point to the Mexican Border and out to 30 nm-Waters from San Mateo Point to the Mexican Border Extending 30 to 60 nm out including San Clemente Island. && $$ PUBLIC...Moede AVIATION/MARINE/BEACHES...Maxwell