Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/24/20

National Weather Service Albany NY
954 PM EST Mon Nov 23 2020 .SYNOPSIS... Lake effect snow showers and flurries will continue to the west and southwest of the Capital District tonight before diminishing towards daybreak. High pressure will move across the area on Tuesday with sunny but cold conditions. Another storm system is forecast to impact the region heading into the Thanksgiving Day holiday with rain and snow showers. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... As of 952 PM EST...A short-wave is moving across the region in the cyclonic flow and a secondary cold front will move through tonight. The low-level flow continues to shift to the northwest and some lake effect snow showers and flurries have grazed portions of the western Mohawk Vally, and currently are moving into the northern and eastern Catskills, and the Schoharie Valley. The low-level flow trajectory and conditional stability class favor some multibands. The inversion heights are low around 5 kft AGL based on the BUFKIT profiles upstream and the latest 00Z KALY sounding. The latest 3-km HRRR continues to show the inversion heights lowering and the flow veering to the northwest, so the activity should continue to diminish 07-10Z. Some light snow accums of a dusting to a half inch are possible in a few locations, and perhaps up to an isolated inch over the higher terrain in a narrow band. A narrow slot of clearer skies has set up along and north of the Mohawk Valley into portions of the Capital Region and southeast into portions of the Hudson Valley, southern Berkshires and NW CT. Some clouds may fill back later. Sky grids were retooled. Also some moisture may remain trapped under an inversion north and west of the Capital District. The winds continue to diminish with the weakening sfc pressure gradient and the stabilizing boundary layer. The clear/partly clouds skies have allow temps to cool off a little quicker in a few spots, so we lowered temps a few degrees with lows still in the upper 20s to around 30F in the valleys, and upper teens to mid 20s over the higher terrain. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... Big Bubble no trouble through Tuesday as 1030+mb surface high slides across the region. Should provide ample sunshine between some stratocu as forecast highs between 40-45F from the Capital Region and points southward with mainly 30s elsewhere (upper 20s for portions of the Dacks). As this high slides off the New England coastline, upstream storm system begins to take shape. This storm, more or less a potent cut off low developing across the four-corners region, will send downstream warm advection regime to unfold. For our region, clouds will be on the increase Tuesday night as broad isentropic lift is expected to take place overnight. Difference this model run and HREF is a more broad potential with overrunning precipitation to evolve toward and after 06Z/Wed. Cross sections from various NCEP Model Suite differ with respect to how much low level dry air will remain in place. Per HREF guidance, we will increase PoPs along and north of I90 with a period of light snow developing. QPF appears to be one tenth of an inch or less. Overnight lows mainly into the 20s. Wednesday, the NAM is the only operational model with surging the warm advection and drier air into the region. Global models suggest the warm front may slow or retreat a bit during the day. The impacts for the region will be either some light precipitation or keeping conditions dry. We will cut the difference and keep the front within the CWA and the low chance for a wintry mix of rain/snow which will be dependent on boundary layer temperatures. Regardless, not expecting too much with QPF consensus generally less than one tenth of an inch. Wednesday night, the aforementioned upper low is forecast to track into the southern Great Lakes region overnight. Low level warm advection and isentropic lift will be across the entire region. Clouds and the threat for additional rain and snow showers, with the better mixture across the higher terrain. Here, the QPF does increase a bit more with the best theta-e advection just to the southeast of Albany. This is where the higher amounts are in the forecast with at or above one quarter of inch with lesser values elsewhere. Overnight lows mainly into the 30s to near 40F closer to the I84 corridor. Thursday (Thanksgiving Day), this upper low is forecast to track across the CWA. This will keep the weather unsettled with additional showers with the best theta-e ribbon to the east of the CWA. At this time, thunder potential looks low as Showalter values do drop but remain around 2C within the global models, near 0C in the NAM south of Albany and mid level lapse rates are moist adiabatic (slightly higher in the NAM). Highs into the 40s with lower half of the 50s from Albany and points south and southeast. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A fairly benign pattern is expected for the long period after a southern stream cut-off low exits our region Thursday night. Temperatures look to run near to even slightly above normal through the period as well. Outside of some possible lake effect snow showers Saturday/Saturday night, the pattern will also generally run dry before attention turns to a potential system early next week that may develop in response to southern stream energy and moisture. Read on for details. Our cut-off low from Thanksgiving exits into New England Thursday night. We continue to show slight chance and low end chance POPS for the Berkshires and Litchfield County before trending dry overnight. Despite the system exiting, west-southwest flow and continued cloud coverage retains the mild air mass overhead which is why we expect overnight lows to only drop into the upper 300s to low 40s. Normal overnight lows for late November are in the mid 20s. By Friday, our 850hPa cold front slowly approaches the region but guidance continues to suggest that weak ridging building in place will maintain zonal/westerly flow resulting in mild temperatures once again. Therefore, expecting highs to reach into well into the 50s with only mid to upper 40s in the higher terrain areas. Guidance is in decent agreement that our mid-level cold front finally pushes through the area on Saturday. While a few upper level shortwaves will act as the needed "kicker" to push the front through the area, the overall upper level forcing remains weak and guidance suggests the front may not move entirely through the area until late in the day. Therefore, temperatures Saturday once again may run a few degrees above normal with highs still in the mid to upper 40s. Normal highs for late November are only around 40. We kept a dry forecast for Friday as well due to lackluster mid-level moisture and weak forcing. Northwest flow in the wake of the boundary finally ushers in a brief period of chillier Canadian air Saturday night. With Lake Ontario still near 10C and 850mb isotherms ranging -3C to -5C, the required 13C temperature difference may barely be met to result in some lake effect snow showers overnight. Given that the chilly air mass will only be overhead for a brief period, we maintained a dry forecast but we will continue to monitor deterministic model trends. Overnight lows finally cool to more seasonably levels ranging from the mid 20s to low 30s. Upper level and surface ridging return for Sunday resulting in another dry forecast. Northwest flow shifts to the southwest which allow temperatures to stay near to slightly above normal in the 40s. Warm air advection increases through the day and into Monday as surface high pressure moves offshore. Forecast confidence decreases heading into early next week as there are notable discrepancies between the deterministic guidance. The GFS and CMC show the potential for northern and southern stream energy to interact which may result in secondary cyclogensis occurring off the eastern seaboard. However the ECWMF show a more suppresses solution which would keep any coastal development well to our south/east. For now, we maintained chance POPs over the region for Monday but it`s worth mentioning that with such a progressive pattern in place, cold air does not look to be readily available. We will continue to monitor trends in the coming days and adjust the forecast as needed. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... An upper level disturbance and a secondary cold front will move across the region tonight. High pressure will build in for tomorrow. VFR conditions are expected the next 24 hours for KGFL/KALB/KPOU/KPSF ending 00Z/WED. Stratocumulus continue at some of the terminal sites with the cyclonic flow and lake moisture being tapped. Cigs are generally in the 3.5-4.5 KFT AGL. Some moisture may remain trapped under an inversion keeping the clouds more persistent at KGFL/KPSF/KALB tonight. Some clearing is likely between 09Z-13Z. KPOU has clouds currently, but these should erode prior to midnight. The subsidence from the strong sfc high will yield clear skies in the late morning through the afternoon. The winds will gradually subside tonight but will still be west to northwest at 5-12 kts, except at KPSF where the winds will be in the 12-18 kt range with some gusts 25-30 kts early tonight before gradually subsiding to around 10 kts with some gusts around 20 kts. N/NW winds will be in the 8-13 kt range during the late morning into the afternoon with some gusts around 20 kts at KPSF/KALB. Outlook... Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Moderate Operational Impact. Chance of SHRA...RA...SN. Wednesday Night: High Operational Impact. Likely SHRA. Thanksgiving Day: Moderate Operational Impact. Chance of SHRA. Thursday Night: Low Operational Impact. NO SIG WX. Friday: No Operational Impact. NO SIG WX. Friday Night: Low Operational Impact. NO SIG WX. Saturday: Low Operational Impact. Slight Chance of SHRA. && .FIRE WEATHER... Colder air moving across the warm open waters of Lake Ontario will bring occasional clouds and some lake effect snow showers to the west and southwest of Albany. Then, high pressure will move across the area on Tuesday. Another storm system is forecast to impact the region heading into the Thanksgiving Day holiday with rain and snow showers. The fire weather season ends today. The issuance of this product will resume in Spring 2021. && .HYDROLOGY... Outside of some light lake effect activity for portions southern Herkimer, Schoharie, Ulster and perhaps into Greene...mainly dry weather overnight into Tuesday evening. Additional wet weather is expected overnight Tuesday into Thanksgiving Day. Amounts won`t be heavy, generally under a half inch, so little hydrologic impact is anticipated at this time. For details on specific area rivers and lakes, including observed and forecast river stages and lake elevations, please visit the Advanced Hydrologic Prediction Service /AHPS/ graphs on our website. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. MA...None. VT...None. && $$ SYNOPSIS...BGM/Wasula NEAR TERM...BGM/Wasula SHORT TERM...BGM LONG TERM...Speciale AVIATION...Wasula FIRE WEATHER...BGM HYDROLOGY...BGM
Area Forecast Discussion
National Weather Service Denver/Boulder CO
819 PM MST Mon Nov 23 2020 .UPDATE... Issued at 819 PM MST Mon Nov 23 2020 Still a very challenging forecast for late tonight and Tuesday morning. The storm total QPF for the 00Z NAM is around 0.87" for KDEN, while the 00Z run of the HRRR is 0.03". A band of heavy snow is expected form due to frontogenesis. Snowfall rates of around 2 inches per hour will be possible under this snow band. Seems the western extent of the models have it over the Denver area. Just eyeballing the models, the average is over the Palmer Divide to northern Washington county. Wouldn`t be surprised to see a small swatch of 5-8 inches if this bands stalls for a few hours. If not, totals should be closer to 2-5 inches. Main message is it will be a snowy slick commute for the Denver area, especially over the western and southern parts. Still haven`t ruled out adding an advisory to areas east of the current one, including Denver. Will wait until the 00Z GFS arrives before making a final decision. && .SHORT TERM...(This evening through Tuesday) Issued at 245 PM MST Mon Nov 23 2020 Satellite imagery shows the increasing southwesterly flow across the state ahead of the approaching trough digging all the way down to southern California. Cumulus clouds moving into the mountains are showing the convective nature ahead of this system, which isolated to scattered showers are expected to continue over the mountains this afternoon and evening, increasing in coverage and intensity toward midnight. Across the plains, the rest of this afternoon and early evening will have high clouds increasing. A surface low will begin dropping south allowing for northerly winds to start spreading across the area with cooler air filtering down. 700-500mb frontogenesis starts showing up well early this evening up across the northern mountains into Wyoming while QG upward vertical motion increases. Showers will be spreading across the plains, but all precipitation should remain rain as the southwesterly flow aloft keeps temperatures warm enough. Not until after midnight, does the actual cold front start plowing down over the area, and the frontogenesis starts moving south as well, with southwesterly flow aloft remaining. Therefore, banding is expected to form across the area, most likely near the I-70 corridor over the mountains northeast out over the plains. Convection is still possible ahead of the front and band, and can`t completely rule out a stronger cell with possible thunder. Forecast soundings show the rain changing over to snow just before sunrise over the metro areas, somewhere between the 3am-5am time frame. The aforementioned convective potential may end up stealing some of the available moisture which may trend down expected snowfall, however, it could also switch the rain over the snow earlier, thereby increasing snow amounts. Needless to say, especially in a banded snow set up, confidence in snow amounts is low to medium. However, still very much agree with the Advisories issued due to upslope flow helping the western and southern suburbs including the Palmer Divide, and the low snowfall amounts will likely fall in a very short time span - being over the morning commute. The band will be able to produce snowfall rates of 1"/hour or more. Initially the snow will likely melt on the relatively warm pavement temperatures, but then create sloppy slush with some areas seeing accumulating snow. The band looks to really have an effect along or south of I-76 corridor and across RMNP and towards Kremmling. North of this, lower snowfall amounts are expected, especially over Larimer and Weld counties due to downsloping off the Cheyenne Ridge. Mountains to the south of the aforementioned area will see the highest amounts, generally 6 to 12", foothills 3 to 7", plains 1 to 3 ", except the western suburbs and southern suburbs down onto the Palmer Divide where 3 to 6 " are expected. The upper trough will be over the area Tuesday morning and move east through the afternoon, bringing subsidence and with drier air moving in from the north. Snow will likely be done and out of the metro areas by noon, with the eastern plains likely seeing it for another couple hours. Some remaining moisture in the northwesterly flow behind the trough will keep light orographic snow across the mountains. .LONG TERM...(Tuesday night through Monday) Issued at 139 PM MST Mon Nov 23 2020 Tuesday night, expect weak subsidence and northwest flow aloft behind the exiting trough, with increasing winds in the mountains and foothills. A strong stable layer will develop over the mountains overnight, with widespread lapse rates around 4 C/km in the 600-500 mb layer. The wind direction is northwest during the strongest flow, so we don`t expect a mountain wave to develop, but are keeping gusts to 40 mph across the highest elevations of the Front Range mountains into midday Wednesday. Forecast soundings are starting to show a few hours of fog around Kremmling in the early morning Wednesday. This has been a common occurrence after snowfall this season so it merits mention and a follow up in a closer forecast period. The ridgetop stable layer and increasing westerly winds aloft will support the development of a mountain wave early Wednesday afternoon, which will amplify through the evening as flow aloft turns more westerly and further strengthens. Strong and gusty winds exceeding 50 mph are probable in the Front Range mountains and foothills but a high wind event is not currently expected. Lee troughing may increase the pressure gradient and cause some of these gusty winds to spread to the adjacent plains in the evening. Subsidence is minimal so the winds will likely remain in and very close to the Front Range foothills. The strong winds should occur late Wednesday into Thursday morning until winds aloft turn southwesterly and decrease in strength. Another trough will come onshore in the Pacific Northwest Wednesday and advance inland through the day. Flow aloft over northeast Colorado will turn southwesterly by Thursday morning as the trough approaches. There will be a slight chance of some light precipitation in the mountains as the trough moves over the Rockies Thursday evening and night. Snow accumulation should be quite limited by a general lack of moisture and modest dynamics. ECMWF and GFS ensembles have only between 0.1 and 0.2 inches of precipitable water in the mountains and a QG analysis of deterministic models showed less than 10 mb/hr of ascent. Lapse rates are favorable for snowfall for only a short time Thursday afternoon, thus only a light snowfall in the mountains Thursday afternoon through Friday morning is expected, with only a few inches accumulating on even the higher ridges. The ECMWF predicts the trough will leave a cutoff low over the four-corners region of the Southwest on Friday as it moves over the Rockies and out to the Plains. Previous GFS runs agreed with this solution, but the latest run is waiting until Saturday morning to drop the cutoff low over Texas and Oklahoma. Thus, there is higher than normal uncertainty in the forecast for this weekend. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) Issued at 819 PM MST Mon Nov 23 2020 Northerly winds are expected to continue through the night and then increase behind a cold front. A few rain showers will develop later this evening, becoming more widespread after midnight. A change over to snow is expected in the 2 am to 4 am time frame. Snow will continue Tuesday morning but should end before noon. At this time, it appears 2-3 inches of snow will possible at KDEN, with 3 to 5 inches at KBJC and KAPA. However, snow banding is expected, so an additional 2 inches will be possible if this band sets up longer than expected. The threat for snow ends around 18Z. By 00Z Wednesday, mostly clear skies are expected to prevail. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 AM to noon MST Tuesday for COZ039- 041. Winter Weather Advisory from midnight tonight to noon MST Tuesday for COZ034-036. && $$ UPDATE...Meier SHORT TERM...Kriederman LONG TERM...Direnzo AVIATION...Meier
Area Forecast Discussion
National Weather Service Des Moines IA
615 PM CST Mon Nov 23 2020 .DISCUSSION.../Tonight through Monday/ Issued at 253 PM CST Mon Nov 23 2020 Forecast Highlights: - Wet and wintry period through the first part of Wednesday - Seasonable and dry Thanksgiving Day - High degree of uncertainty in forecast late next weekend Details: GOES-East upper level water vapor imagery shows a deepening trough over the Intermountain West early this afternoon with our area under the influence of a 250mb, ~100 knot, favored for ascent left exit region. As this trough and a developing area of surface low pressure over eastern Colorado moves eastward today, will see precipitation trying to lift into our area. However, this will first have to overcome a good deal of dry air in the atmosphere, which has occurred with strong lift over southern Iowa late this morning and early this afternoon. The 12z OAX RAOB showed this dry air below 450mb, but some saturation was beginning to occur in a shallow layer around 700mb. Subjectively, the HRRR and RAP soundings seemed to verify best with the observed sounding with the NAM and GFS to a slightly lesser degree. The key will be how quickly saturation is achieved, especially with temperatures rising to above freezing. Early morning runs from the HRRR and RAP point to early this afternoon for top down saturation to occur versus late afternoon/early evening from the NAM and GFS. With snow just beginning at our office just before 2pm, the winners are the HRRR and RAP. With the dry air, wet bulbing has been occurring, which has resulted in a half inch to inch accumulations in our southwest forecast area so far. Most of this snowfall will accumulate on grassy areas with some accumulation on roadways if rates can last long enough to overcome above freezing road surfaces. This wave of isentropic lift on the 290-295K layer will eventually lift eastward through this afternoon with primarily snow continuing. Some light rain is possible, but given we are on the downward slide of peak heating and dewpoints are hanging in the upper 20s to 30s at this hour, that will not be common. Another wave of isentropic lift, which looks even stronger and is coincident with strong QG convergence, will move over Iowa tonight. There will be strong moisture transport into the state for late November with precipitable water values ranging from 0.75" over northern Iowa to around 1" over central/southern Iowa. While southern Iowa will predominately see rain as this low level thermal lift prevails, for northern areas a transition to snow is likely. Forecast soundings over northern Iowa (e.g. MCW, ALO) reveal that while surface temperatures may be at or just above freezing, there is a deep layer in which the temperature profile is in the favored dendritic growth zone just below freezing with lift maximized toward the middle to top of this layer. This transition to snow will occur this evening through the hours around sunrise before transitioning back to rain. The snow may come down heavily for a time, with the 3z/9z SREF having a small area topping out with probabilities of 40- 50% of 1"/hr rates that develop over our far northeast CWA and more so points north and east as it departs our area tonight 6-12z tonight. The 12z HREF has very low, splotchy 1"/hr probabilities as well, but most of that is over northeast Iowa as well. While ground temperatures and perhaps even the surface temperature may be 33/32, the expected precipitation rate at night will overcome this and cause accumulation. This snowfall will have low snow to liquid ratio and be wet and sticky given the thermal profile near 0C. There is potential that if profiles cool quicker this evening and last long with modest to high rates that accumulations would be higher. While the timing lowers the impact with the exception of the morning rush hour, the uncertain in borderline temperature profile leads us to, in collaboration with WFOs La Crosse and Quad Cities, to issue a winter weather advisory later this evening through the morning rush hour over our northeastern areas. Accumulating snowfall will switch to rain through the morning hours with any impacts from the snow lessening with time as temperatures rise above freezing. The rain will generally be on the lighter side and may at times turn to more of a drizzle, especially over northern Iowa. As another area of strong QG convergence moves through northern Missouri and southern Iowa later Tuesday into Tuesday night ahead of the trough and surface low, will see return to more persistent rain. The deformation zone on the back side of the low will have precipitation and soundings still largely support in the form of rain with GFS showing the most low level warm air as far as depth and magnitude compared to NAM. As this surface low moves from Missouri into the western Great Lakes Wednesday, this will bring an end to the precipitation. Thanksgiving Day will be dry as a moisture starved front passes with lower thicknesses following behind and a cooler day on Friday with highs about 5 degrees lower. Highs will be slightly higher on Saturday ahead of the next weather system, which deterministic and ensemble members disagree on the handling of. The 00z ECMWF and the 12z CMC phases the north and a southern stream wave and generates wintry precipitation over at least part of the state on Sunday. The 06z/12z GFS and 12z ECMWF has the northern and southern stream farther apart and phasing never occurs yielding a dry forecast. 00z ensemble members are split as well so going forecast will not deviate from initial guidance. Until the resolution of these differences, there is a high degree of uncertainty in the temperature forecast ranging from the upper end in the 40s to the low end in the upper teens or 20s. && .AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/ Issued at 607 PM CST Mon Nov 23 2020 Poor aviation conditions abound at area termianls over the next 24 hours as an area of low pressure takes aim on the state. The period begins, with ongoing area of -SN mainly east of I-35 and south of I-80, primarily impacting KDSM and KOTM with generally 1-5SM VSBYS. Northern IA terminals will see deteriorating conditions through 06z as CIGS lower and precipitation expands across the area. KALO will see the most snow accumualtions 04-12z, with generally 2-3" expected there. Elsewhere snow will transition to -RA from SW to NE overnight. This trend continues even at KALO for the daytime hours on Tuesday. Low CIGS and -RA will persist through the day however. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 10 PM this evening to 8 AM CST Tuesday for IAZ007-017-026>028-037>039-050. && $$ DISCUSSION...Ansorge AVIATION...Hahn
Area Forecast Discussion
National Weather Service Grand Forks ND
839 PM CST Mon Nov 23 2020 .UPDATE... Issued at 839 PM CST Mon Nov 23 2020 Surface temperatures in southeast North Dakota remain quite mild early this evening. The increasing low clouds in that area and steady southeast winds will likely keep temperatures steady or slightly rising overnight. Went ahead and blended in the latest HRRR temperature guidance for all areas overnight, which has the same idea of steady or slowly rising temperatures. Looking at some of the road temperature forecasts, portions of east central and southeast North Dakota stay above freezing overnight. Therefore, thinking if any drizzle forms, it would only be freezing north of highway 200 in North Dakota and across most of the northwest quarter of Minnesota. UPDATE Issued at 615 PM CST Mon Nov 23 2020 Low clouds are poised over eastern South Dakota and southwest Minnesota, and they have been creeping into the far southern Red River Valley. Temperatures are pretty mild under this band of clouds, and have yet to see any stations reporting anything falling out of them. Models are still indicating the potential for some light precipitation (rain/freezing rain/snow) as these low clouds work northward late tonight into Tuesday morning. At this point, see no reason to play too much with the forecast. && .SHORT TERM...(This evening through Tuesday night) Issued at 343 PM CST Mon Nov 23 2020 Fair skies and breezy southeast winds will persist through the remainder of the afternoon and evening, with overnight low temperatures slowly settling into the 20s overall, but staying nearer the thaw point along the SD border area and into west central MN. At the surface, and inverted trof will build into the area as a low pressure system, now in far northeastern CO, steadily pushes up into the northern plains region. The main arc of precipitation from this storm system will spread across southeastern SD and southern MN through the day on Tuesday, while the inverted trof anchors into northwestern MN and pulls some moisture and energy to the area. Expect increasing clouds during the overnight period with areas of light freezing mist or drizzle developing from southeastern ND into westcentral and northwest MN throughout the early morning on Tuesday. Gusty southeast winds will persist through he morning at from 10 to 20 mph, but turn from the south by midday, and eventually turn from the northwest through the afternoon. Daytime highs should rise into the lower to mid 30s across the northern tier, and reach the upper 30s to around 40 degrees in the southern Valley. Precipitation amounts should range from trace amounts into a few hundredths of an inch of freezing drizzle and rain, with a slight amount of snowfall possible along and north of Highway 2, mainly in northwest MN. This system should progress steadily eastward through the day, with clearing skies moving in from the west, behind a cold front, through the late afternoon and early evening. Seasonably cool and dry conditions are expected Tuesday night into Wednesday. .LONG TERM...(Wednesday through Monday) Issued at 343 PM CST Mon Nov 23 2020 Overview... Clouds linger into Wednesday morning as a trough moves east of the Northern Plains into the Great Lakes region. General trend of quiet weather ensues across the forecast area during the end of the week and into the weekend. Some areas in the western portion of our region could see several occurrences of windy afternoons. No impacts are expected to the region. Wednesday through Thursday... Clouds linger through Wednesday morning, with a gradual clearing by the afternoon as a ridge builds into the Northern Plains. There exists the potential for some gusty winds Wednesday and Thursday across portions of the northwestern forecast area. Soundings indicate some inverted "v" structure in the lower levels and slight mixing from the 850mb height. Winds have the potential to gust toward 25-30mph in the Devils Lake region. Other than some wind potential impact is little to none across the forecast area, with temperatures remaining seasonal as highs hit the low 30s toward Fargo. Thursday is slightly warmer with mid 30s north and low 40s in the south under mostly sunny skies. Friday and beyond... A pattern of quiet weather continues throughout the weekend into the early part of next week, with above normal temperatures to start the weekend and a return to normal by the end. A low pressure system moves north of the region across Manitoba during Friday into Saturday, with a slight possibility of the trailing cold front bringing flurries to the northern portions of the forecast area. Models are in disagreement in the amount of moisture available and the exact track of the system in Manitoba. The trailing cold front on Saturday brings our temperatures back to seasonal averages for the end of the weekend and into the first week of December. Pressure gradients tighten from the passage of the cold front, increasing winds across the forecast area. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 615 PM CST Mon Nov 23 2020 Lots of things to watch in the aviation forecast. Low clouds are expected to stream northward tonight, bringing most TAFs into IFR conditions. Unless fog forms, do not think visibilities will get restricted. Winds will stay fairly steady, switch to the south Tuesday morning, then switch to the west by Tuesday afternoon. Finally, there may be some light rain/freezing rain/snow overnight into Tuesday morning. Confidence not too high on timing or what type of precipitation it may be. Will be watching what happens further southward to get an idea of what may occur. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. $$ UPDATE...Godon SHORT TERM...Gust LONG TERM...Spender AVIATION...Godon
Area Forecast Discussion
National Weather Service Goodland KS
756 PM MST Mon Nov 23 2020 .UPDATE... Issued at 755 PM MST Mon Nov 23 2020 Updated precipitation chances slightly for Tuesday morning and afternoon. Precipitation chances are expected to increase in the northwestern part of the area Tuesday morning, with a second area of chances increasing in the southeastern part of hte forecast area in the afternoon. As temperatures rise, there may be a brief period of light freezing rain in eastern Colorado. && .SHORT TERM...(This evening through Tuesday) Issued at 1254 PM MST Mon Nov 23 2020 19Z Water vapor imagery and RAP analysis indicated strong short wave trough approaching the four corners area. This system will be the primary driver of tonight through Tuesday`s potential precipitation. At the surface, strong sfc trough deepened across eastern Colorado as much of the area was covered by thick clouds. Strong southerly flow was noted across the southeastern portion of the area where winds were gusting in excess of 40 mph in some locations. Main forecast concern will be precipitation and potential for winter weather impacts through the evening Tuesday. Lots of uncertainty with respect to how this system will evolve and the first major change to going forecast is to slow precipitation onset down by 3-6 hours. Despite some elevated instability, bulk of short term models support a very dry layer of air persisting through much of the overnight period, especially to the north of cold front. While it is possible that this level could saturate earlier and lead to precipitation, think overall pattern supports a slower evolution/development for precipitation given the overall moisture profile. While there is pretty good agreement with overall system evolution and timing, the presence of elevated instability increases uncertainty with respect to amounts and may create a situation with spotty higher amounts surrounded by relatively little precip. Current thought with respect to precipitation evolution have me leaning towards seeing two distinct areas of precipitation initially. The first will be across northeast Colorado along strong frontogenetic circulation. Synoptic scale support stronger south and west so think best response will be just to the west of the forecast area. A second area will develop near the surface front as saturated low level airmass may support some weak instability, with a thunderstorm not out of the question during the morning and early afternoon hours. As H5 trough nears the area, expect northern area to shift south and gradually consolidate with precipitation area across southern CWA. Right now, think this area will diminish as it moves south so there may be an area that receives relatively little precipitation through the day. With up to 500 j/kg of mucape available, could see areas with more significant rain and even convective driven snow, but these should be very isolated with threat for heavier snow or precipitation small. Think the biggest potential impact for snow will be between Burlington and Limon between 12 and 21 UTC, where 1 to 3 inches of total accumulation possible. Given overall poor snow growth profiles and uncertainty with precipitation placement, do not anticipate any highlights for snow at this moment. Precipitation should come to and end quickly after 00z as trough axis moves well to the east of the area and strong downward motion will overspread the area. As skies clear and winds relax, expect a chilly night with lows approaching the teens in some areas. .LONG TERM...(Wednesday through Sunday) Issued at 113 PM MST Mon Nov 23 2020 Wednesday... An upper level ridge is expected to move over the High Plains beginning Wednesday morning bringing dry conditions to the Tri-State area. Guidance is in good agreement that the ridge will move quickly across the Plains throughout the day as our next trough system pushes across the western CONUS. Late Wednesday night, the upper level winds will shift to the SW as the trough digs into the Southwest region. At the surface a trough will develop over eastern Colorado during the afternoon hours, forming a closed low across the TX-OK panhandles and western Kansas overnight. Temperatures on Wednesday are forecasted to reach the low to middle 50s for highs and drop into the low to middle 20s for overnight lows. Thursday... The Tri-State area will continue to experience SW flow aloft through Friday as the positively-tilted upper level trough continues to move east. A cold front is expected to move across the area Thursday morning from the northwest. The timing of the front is earlier compared to the previous forecast, but the timing could still change over the next few days. If the front follows the current guidance, high temperatures could be cooler than currently expected. As mentioned in the previous discussion, there is little moisture associated with this front. The surface low and trough that formed south of the area Wednesday night is currently expected to continue east along the Kansas-Oklahoma border. As the low moves east, the models are showing an increase in moisture over the eastern half of the CWA Thursday afternoon. Despite the added moisture, the area should remain dry. The high temperatures are expected to range from the 40s to low 50s, with cooler temperatures possible depending on the cold front. Low temperatures are expected to fall back into the upper teens to mid 20s overnight. Friday... This is where it gets messy with the models. Both the GFS and the ECMWF are continuing to depict the trough finally moving over the CWA throughout the day on Friday. However, the ECMWF has a different solution with the formation of a closed low over the Four Corners region at the base of the deep trough. At the surface, high pressure is expected to move over the Central Plains, keeping the region dry through the early afternoon. During the late afternoon and evening hours, chances are currently expected to increase, mainly south of US-40, for a light rain/snow mix that becomes light snow as temperatures drop. Little to no accumulations are expected at this time. Temperatures on Friday are currently expected to range from the 40s to low 50s for highs and low 20s for lows. Saturday and Sunday... The models continue to disagree on the upper level pattern and the location of the trough. The GFS has the trough moving SE out of the area Saturday morning, followed by a ridge with surface high pressure. The ECMWF has the closed low just SW of the area near the CO-NM-TX-OK border. The ECMWF keeps the low stationary in that general area through the end of the extended period. With the models differing on the location of the trough, there is also disagreement on precipitation this weekend. The GFS keeps the area dry through the end of the period, while the ECMWF keeps precipitation mainly south of the CWA from Saturday morning through late Sunday morning. There is a window during the overnight hours Saturday into early Sunday where areas south of I-70 could see some precipitation. Due to the uncertainty with the models, the confidence in any precipitation occurring is low. For now, sticking to less than 25% for PoPs. There is a slight chance for light snow across much of the area early Saturday. As temperatures slowly climb with daytime heating Saturday, the snow could transition to a light rain/snow mix before becoming completely rain in the afternoon. We could see another transition from rain to snow during the evening hours through Sunday morning as temperatures drop and another cold front passes through the area. Precipitation chances should decrease throughout the morning from west to east before exiting the area completely around mid-day. High temperatures on Saturday will be in the 50s, with lows in the 20s. Sunday will be colder due to the frontal passage, with highs only in the low to mid 40s. Low temperatures are expected to range from the mid teens to low 20s. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 434 PM MST Mon Nov 23 2020 VFR to IFR conditions forecast for the TAFs. Conditions for KMCK are expected to deteriorate over the next hour as MVFR ceiling from the southeast moves in. There may be an hour or two window during the evening when the ceiling improves to VFR, however confidence of that occurring is too low to put in the TAF. Otherwise IFR conditions will move in around 8z for KMCK, with MVFR conditions for KGLD. These MVFR conditions may be short lived, and quickly fall to IFR for KGLD. These conditions will persist into the morning before beginning to improve to MVFR. Conditions will improve to MVFR when the precipitation begins. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ UPDATE...AW SHORT TERM...JRM LONG TERM...KMK AVIATION...JTL
Area Forecast Discussion
National Weather Service Wichita KS
556 PM CST Mon Nov 23 2020 .SHORT TERM...(This evening through Wednesday night) Issued at 419 PM CST Mon Nov 23 2020 Highlights: 1) Drizzle tonight changing to showers Tuesday 2) Thunderstorms Tuesday evening in southern KS - strong to severe possible 3) Rain/snow mix or snow possible in north central KS Tuesday night 4) Temps in upper 50s Tuesday and low 50s Wednesday Challenges: 1) Temperatures on Tuesday 2) Timing of post frontal cold air on Tuesday Changes: 1) Increased/modified precipitation chances 2) Increased precip chances Tuesday afternoon with quicker exit As moisture transport continues to increase through Tuesday, this will help saturate the low levels. Anomalies for precipitable water values indicate the same two to four standard deviations above normal from this evening into Tuesday evening. Model soundings indicate drizzle will be possible tonight before complete saturation of the column occurs late tonight into early Tuesday. At that time, there will be larger droplets with a change to showers and increasing chances for precipitation around daybreak and through the day. The previous discussion pointed out a similar challenge of the daytime temperatures given the cloud cover and precipitation but an aid of low level warm air advection; forecast high temperatures fit with the general consensus of most models albeit just a tad higher with minimal changes from the previous forecast. The trough over Great Basin maintains its eastward trajectory and is still on target to move through on Tuesday. This is the most notable system within the forecast as the path is directly east across Kansas. As the system moves into the Plains, it closes off or essentially strengthens. The forcing associated with this low combined with the instability/shear should result in thunderstorms as has been noted for the last several days. There is some surface instability (~500 J/kg) at its peak unless you believe the RAP which has values closer to 1k J/kg. Shear appears to the greater indicator with roughly 40-60kts on hand. The focus for the convection appears closely tied to the front and its respective passage which would put a peak time in the early evening hours (~0Z or 6PM) for south central Kansas. As the Storm Prediction Center has indicated in their updated Day 2 Outlook, the potential area for a few strong to severe thunderstorms will be in southern Kansas with the better potential in Oklahoma based on the addition of a slight risk. Bulk shear vectors are nearly parallel to the cold front which would suggest convection to be more linear in nature. In Kansas, the threats are nickel to quarter sized hail and 50-60 mph winds. As cold air is ushered behind the front, this could result in a mix of rain/snow or snow across north central and northwest Kansas Tuesday night into early Wednesday. Drier air moves into the mid levels during this time which would limit the window for a mix or snow. On the other hand, a quicker arrival of colder air would increase the longevity for snow and potential accumulation given the steep lapse rates/lift as the last discussion mentioned. Surface soil temperatures are still in the 40s which would help. Given the current expectations, minimal if any accumulation is anticipated at this time. Any minimal accumulations would not last long given those temperatures and air temperatures above freezing Wednesday morning. The system will push east and northeast to the middle Mississippi River Valley by mid day Wednesday. Therefore precipitation should end by Wednesday morning before sunrise. Clouds should clear out through the day, and high temperatures should be about seasonal normal in the lower 50s. .LONG TERM...(Thursday through Monday) Issued at 419 PM CST Mon Nov 23 2020 Highlights: 1) Thanksgiving forecast: Temps - low 50s to near 60. No precip 2) Slight chances of precipitation in southern KS Fri eve-Saturday 3) Temperatures in the upper 40s to mid 50s Friday to Sunday Thanksgiving forecast: Overall it will be a fairly nice day. High temperatures are forecast in the lower 50s in north central Kansas to around 60 along the Kansas/Oklahoma border. This will be near or above the climatological normal values. No precipitation is expected. Scattered clouds will be combined with winds at 10 to 15 mph. Thus it will be a good day to talk a walk or do some other outdoor activity before or after your meal. A weak wave is progged to move through on Friday with slight precip chances moving in Friday night. There is no change in the differing model solutions. The ECMWF shows a quicker to deepen solution closing off its low near the Desert Southwest while the GFS is the slower solution and further to the south. Both models indicate a southeast track and keeping the main system to the south. Given this variability, the slight chances seem to be representative for now. Cool air advection may move in Sunday to cool down the start of next week with high temperatures down to the mid 40s. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 555 PM CST Mon Nov 23 2020 Main concerns: LLWS overnight, IFR/LIFR flight conditions across the area, and northerly wind shift in central KS toward the end of the TAF period. Marginal LLWS possible at most sites overnight, though breezy sfc winds will likely limit LLWS at times. Ceilings will continue to drop overnight area as strong moisture advection is ushered in. Expect widespread IFR conditions and periods of LIFR conditions, except at KCNU which should be delayed and remain near MVFR through late tomorrow morning. Winds will remain out of the south until the cold front arrives tomorrow afternoon. The northerly wind shift should arrive in central KS in the 18-21Z timeframe tomorrow. Precipitation wise- Periods of light drizzle will be possible overnight which could temporarily reduce vis, but left out of TAF for now given scattered nature. Thinking remains that the area will remain mixed enough to not develop much, if any, fog. Expect scattered showers and storms tomorrow along and ahead of the cold front. A few storms tomorrow late afternoon to early evening could be strong to severe with nickel to quarter size hail and wind gusts to 60mph. && .PRELIMINARY POINT TEMPS/POPS... Wichita-KICT 47 58 35 51 / 50 80 70 0 Hutchinson 47 58 33 51 / 50 80 70 0 Newton 46 56 34 50 / 50 80 80 10 ElDorado 47 57 36 50 / 60 80 90 10 Winfield-KWLD 48 58 36 53 / 60 80 70 0 Russell 46 57 29 49 / 40 80 60 0 Great Bend 46 58 30 50 / 40 80 60 0 Salina 46 57 33 49 / 50 90 90 10 McPherson 46 57 32 49 / 50 80 80 10 Coffeyville 47 58 40 54 / 50 80 90 10 Chanute 47 56 40 51 / 50 80 90 10 Iola 46 56 39 51 / 50 80 90 10 Parsons-KPPF 47 57 41 52 / 50 80 90 10 && .ICT WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...VJP LONG TERM...VJP AVIATION...KMB
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
905 PM CST Mon Nov 23 2020 .UPDATE... 905 PM CST The overall forecast looks on track this evening. 00Z ILX/DVN RAOBs and recent MDW AMDAR soundings reveal a substantial amount of dry air in the 750-900 hPa layer across northern Illinois. This instills some concern of the behavior of the initial precip band at the surface, with the potential for pockets of heavier precip instead of a solid line shifting northeast across the area during the overnight hours. With that said, latest hi-res guidance still supports moderately to briefly heavy snowfall rates for a 1-2 hour period at onset with the initial band. Have therefore opted to make very little change other than to tighten the PoP gradient on the northeast side of the precip band through daybreak Tuesday. Additionally, have moved up the start time of the advisory for Ogle and Lee counties to midnight as moderate to briefly heavy snow may be ongoing as early as around 1 am. Kluber && .SHORT TERM... 310 PM CST Through Tuesday night... The first Winter Weather Advisory of the season has been issued for parts of the far west and northwest Chicago suburbs, out to north central and northwest Illinois portion of the CWA. Advisory was issued in collaboration with WFO DVN and MKX to emphasize impacts to travel during the morning commute, including slick/slushy spots on some roads and visibility as low as ~1/2 mile at times. Most of the CWA except parts of the far south should have a period of all snow as precipitation type and low visibility from this event. However, with more marginal >32F surface temps and overall lower snow totals forecast, impacts should be mitigated. A potent mid/upper level impulse over the Great Basin region will be the primary driver of the weather system set to impact our local weather through Wednesday. A developing surface low across the front range of the Rockies is occurring in response to the mid/upper level short-wave digging into the Four Corners region of the southwest CONUS. The associated downstream southerly low- level mass response will drive a southerly 50+ kt low-level jet from the Plains east-northeastward into the Upper Midwest tonight into Tuesday, resulting in a rapidly northward shifting plume of deep Gulf Moisture into the region. This will set the stage for rapid precipitation development into the area later tonight, despite antecedent very dry air aloft. The area of precipitation will blossom and/or expand northward across the CWA overnight as warm advection and isentropic ascent become quite robust. As alluded to in intro, precipitation type is expected to be mainly in the form of snow for most of the area for at least a few hours after midnight through the early morning. With baroclinic zone oriented from northwest to southeast and continued strengthening warm advection will gradually transition p-type to rain from southwest to northeast. The warming aloft will gradually offset dynamic cooling processes along with an easing of forcing as a lead positive tilt wave shifts northeast of the area. While it can`t be ruled out that some sleet may briefly mix in during the transition, the increasing southeast surface winds should lead the surface temps to rise safely above freezing as the >0C air aloft rushes in. Thus, think that p-type transition for most locations will be one of snow to rain. While the window for steady snow with this system will generally only be for about 3 to 6 hours for most locations, there is increasing concern that the rates could be moderate, to even briefly heavy into early Tuesday morning, thus accumulations appear likely for many areas of northern IL inland from the lake, and this would impact the Tuesday morning commute. Forecast soundings, especially from the NAM/WRF guidance and RAP have an approximate 2-4 hour window of good co-location of very strong omega through the DGZ, which is a favorable look for moderate to briefly heavy snowfall rates. Looking more in depth, model guidance continues to suggest that a stout, but transient band of 700-500 MB frontogenesis will develop northward into the area very late tonight into early Tuesday morning. The associated ageostrophic response should force good ascent right through the favored dendritic growth zone, as noted above. This in combination with very steep lapse rates through this layer from around 600 mb through 400 mb suggest that the snow may fall at a heavy rate for a couple hour period early Tuesday morning. There is even support for larger snow flakes due to aggregation processes in the lower-levels, resulting from a deep moist isothermal layer just below 0C from the surface to just above 700 mb. This could thus support accumulations on some area roads, in spite of marginal surface temperatures, so impacts to the Tuesday morning commute look probable, especially outside the main urban center of Chicago. Exact response of road temps to heavier snow rates is uncertain, but with signal for strong dynamic cooling evident, think that surface temps will be kept around 32F. This should enable for slushy accums on some roads, especially lesser traveled secondary roads and bridges. Total snow accumulations look to be in the 1-3" range I-80 and north in Illinois and roughly along/west of I-294, with little/no accumulation along the lakefront in Chicago. Can`t rule out some isolated >3" amounts closer to the Wisconsin border within advisory area where change to rain will be the latest. Any accumulation in the city stands to predominantly be on grassy/colder surfaces and main travel impact would be from the lower visibility. Speaking of visibility, favorable factors listed above will also be favorable for periods of visibility below 1 mile during the heaviest snow, possibly as low as 1/2 mile at times. All in all, with the greater impacts to the commute likely focused into interior northern Illinois, opted to issue the Winter Weather Advisory for McHenry, Kane, DeKalb, Winnebago, Boone, Lee, and Ogle Counties, in effect from 2AM to 10AM. After the transition to rain clears the entire area to the north, there will be continued periods of rain of varying intensity through Tuesday night. As the surface low pressure area moves closer after midnight Tuesday night, temperatures in the lower to mid 40s and similar dew points (little/minimal T/Td spread) will mean saturated low levels and a chance for fog development. Especially where rain rates become light coupled with lighter winds, will have to monitor the potential for patchy dense fog in spots. There was a signal for this on some of the MOS guidance in parts of northern Illinois. Castro/KJB && .LONG TERM... 158 PM CST Wednesday through Monday... Extended forecast highlights include mid-week rain, quiet and relatively mild weather for the Thanksgiving holiday into the weekend, then a low-confidence but potentially unsettled period Sunday into Monday with a push of colder air early next week. Guidance remains in good agreement in depicting a closed upper level low near Kansas City early Wednesday, nearly stacked atop its associated occluded surface low. Low level southerly winds ahead of this circulation will continue to advect Gulf moisture into the region during the day, maintaining rain/shower threat as the low tracks northeast across the southeastern part of the WFO LOT cwa by late afternoon. A couple of areas of better focus for precipitation and higher rainfall amounts are noted, one across our southeastern counties where unseasonably mild/moist (temps in the mid-upper 50s and surface dew points around 50) in the vicinity of the triple point of the occlusion will reside, and a second farther north across northwest and far northern IL where better baroclinicity exists along an inverted cold frontal trough north/northeast of the low. Forecast soundings continue to depict some weak MUCAPE across our southern counties Wednesday afternoon near the triple point, worthy of at least some slight chance thunder mention there. Rain should taper off and end from west to east Wednesday evening as the upper trough and surface low move off to the east of the forecast area. Weak surface high pressure ridge moves in behind the departing system late Wednesday night into Thanksgiving day, though given the occluded nature of the departing low there is not much of a push of cooler air, and no deep/strong subsidence to erode lingering low level cloud cover. It will be dry and relatively mild for the holiday however, with high temps around 50 degrees expected. Quiet weather looks to persist through the end of the week and into at least the first half of the weekend, as large scale upper trough becomes positively-tilted across central and western North America. Similarly dry and relatively mild conditions appear in store for the region again Friday and Saturday. Models have shown some significant differences with the evolution of the upper pattern later in the weekend into early next week. Guidance is in generally good agreement in closing/cutting off an upper low across the southwestern CONUS by the weekend, while the northern portion of the aforementioned upper trough progresses eastward with a dry pacific cold frontal passage across our area Friday. Previous runs of the ECMWF and GEM then depicted another upper trough phasing with the southern closed low and developing a strongly amplifying upper trough and deep low surface low which would affect the Midwest Sunday-Monday. 12Z runs of these models have trended toward the GFS solution of a somewhat more progressive southern stream low and no phasing/impressive amplification of a deeper trough across the Midwest. Getting a look at 12Z ECMWF ensemble mean does still spread some lighter precip across especially our south/southeastern cwa Sunday/Sunday night, so am a bit hesitant to pull pops completely during that period so will maintain some slights/low chance focused on Sunday/Sunday evening. Could be some rain/snow mix in colder evening hours, though mainly rain expected with temps well above freezing (40s) during the day. Ratzer && .AVIATION... For the 00Z TAFs... 548 PM...Forecast concerns include... A period of moderate snow predawn hours thru mid morning. Rain showers for the rest of the period. Ifr cigs Tuesday morning...lifting to low mvfr in the afternoon. Gusty southeast winds Tuesday. An area of snow currently over southern IA and northern MO will continue moving northeast and will reach the terminals in the predawn hours. Current timing in the tafs looks on track. Vis/ cigs should quickly drop into ifr as the snow begins. There may be a 1-2 hour period of vis in the 1/2sm range along with lifr cigs. As the precip intensity begins to diminish by mid morning...the precipitation will mix with then change to light rain. Medium confidence on this timing. Ifr cigs are expected to lift to low mvfr for the Chicago terminals...but ifr will be nearby to the northwest. Ifr cigs are possible at ord/ least for a time Tuesday afternoon. Rain showers will continue Tuesday afternoon into Tuesday night. Eventually cigs will lower back to ifr Tuesday evening. Easterly winds will turn southeast later tonight with speeds increasing to 10-12kts. Winds will remain southeast Tuesday with some gusts into the 20kt range. Winds will slowly turn more southerly Tuesday evening. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Winter Weather Advisory...ILZ008-ILZ010...midnight Tuesday to 10 AM Tuesday. Winter Weather Advisory...ILZ003-ILZ004-ILZ005-ILZ011-ILZ012...2 AM Tuesday to 10 AM Tuesday. IN...None. LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744- LMZ745...9 AM Tuesday to 6 AM Wednesday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Miami FL
811 PM EST Mon Nov 23 2020 .Update... Generally quiet conditions across South Florida in the short-term, as a weak surface front continues to move southward through the remainder of our area. Along and behind this boundary, isolated showers continue to develop over the Atlantic waters off South Florida, where marginal surface-based instability remains in place (owing to lingering dewpoints in the upper 60s F and moisture fluxes atop the Gulf Stream). In addition, 40 knots of mid-level flow is supporting enhanced bulk shear over the Atlantic waters, which has allowed for periodic organization (mid-level rotation) within some of the above mentioned convective showers. The primary concern with this activity has been waterspout potential and brief gusty winds, though the latest RAP mesoscale analysis and 00Z MFL RAOB suggest that the instability is becoming elevated, which will limit the overall waterspout risk with time. As the surface front continues southward, dry air will continue to filter into South Florida, as a mid-level high builds over the eastern Gulf of Mexico. This combination should support strong subsidence and an associated warm/dry layer aloft -- suppressing most convective development during the day on Tuesday. Winds will continue to transition from a northerly direction to an east-northeasterly direction while the pressure gradient tightens behind the above mentioned surface front. The onshore flow component and enhanced pressure gradient will support breezy conditions tomorrow, especially along the east coast of South Florida. This will also support a lingering elevated rip current risk along the east coast beaches. Temperatures will remain near-normal or slightly below average (mainly inland/SW FL), while dewpoints in the 60s F tomorrow should support a fairly comfortable day. && .Prev Discussion... /issued 702 PM EST Mon Nov 23 2020/ Aviation (00Z TAFs)... Primarily VFR through the period, though isolated SHRA could linger along the east coast of S FL overnight. Any impacts from this activity should be limited. NNW flow will will continue to transition to NNE, becoming breezy during the day tomorrow. Prev Discussion... /issued 342 PM EST Mon Nov 23 2020/ Short Term... Today Drier air advecting over the region today, as a 500 hPa ridge of high pressure progresses over the Florida panhandle. The eastern periphery of this ridge will induce cold air advection over the region, further supported by pressure rising at the surface. Isolated showers will be generally confined over the Atlantic waters and along the coast, with 15-20 PoPs over the aforementioned areas. Meaningful accumulations are not anticipated with any developing showers. Rain chances will decrease further Tuesday with a surface trough moves through the region, as dry conditions are anticipated over South Florida. Maximum temperatures are forecast to be seasonably cooler, with upper 70s/lower 80s across the region. With a low-level trough forecast to progress over the region Monday night/Tuesday morning, a north/northeasterly wind will cause a drop-off in dewpoints temperatures and hence a slight decrease in apparent temperatures as well. Long Term... .Tuesday Night through Sunday... Benign, dry, and seasonal conditions will continue to prevail across South Florida for the remainder of this week, as a ridge of high pressure aloft becomes established over our area. The weak frontal boundary that traversed across our area earlier today will continue to drift towards the south and will dissipate over the Florida Straits as airmass modification continues to occur to the north of the boundary. With high pressure in firm control this week, model consensus continues to keep a cold front well to the north of our area. As the high slides eastward during this week, upper-level zonal flow across the region will be of westerly orientation. At the surface, easterly winds will prevail. As precipitable waters values during the first part of this week are within the 1.0 to 1.4 inches range, isolated showers along the adjacent Atlantic waters and the east coast of South Florida cannot be ruled out. During the remainder of this week, high temperatures will continue to be in the low 80s across our area with overnight temperatures in the upper 60s to the low 70s. .Sunday Night through Monday... While there is considerable uncertainty in long-term model guidance, current indications point to the approach of a strong cold front towards our area early next week. With the potential passage of this strong cold front across our area, this portion of the forecast period will be important to monitor for potential weather impacts and changes in forecast. The timing and strength of the cold front will dictate the potential low and high temperatures during this portion of the forecast period. Marine... A surface trough will progress through the Atlantic and Gulf waters today. Winds are forecast to change direction from northerly to northeasterly across the local waters as the front continues to move southward. A Small Craft Advisory is in effect for the offshore Atlantic waters through at least Tuesday. This advisory could expand towards the nearshore waters and may require an extension beyond Tuesday depending on how conditions evolve with time. Beach Forecast... With decreasing easterly flow, rip currents become less favorable today. However with the wind direction shifting from north to northeast with a passing surface trough, a moderate risk for rip currents will remain through at least Tuesday for the Atlantic beaches. && .Preliminary Point Temps/PoPs... West Palm Beach 70 79 69 80 / 10 10 0 0 Fort Lauderdale 71 81 72 81 / 20 20 0 0 Miami 70 81 71 82 / 20 20 20 0 Naples 64 84 66 83 / 0 0 0 0 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...None. AM...Small Craft Advisory until 7 PM EST Tuesday for AMZ670-671. GM...None. && Update...18/Weinman Aviation...18/Weinman
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
621 PM CST Mon Nov 23 2020 .UPDATED for 00Z Aviation Discussion... Issued at 617 PM CST Mon Nov 23 2020 && .SHORT TERM...(This evening through Tuesday night) Issued at 254 PM CST Mon Nov 23 2020 Weak high pressure atop the region, responsible for the plentiful sunshine experienced across the region today, will slide off to the east with a potent but compact low pressure center on its heels. This system will be kicked northeast from the lee of the Central Rockies with the help of a digging and merging trough moving away from the western CONUS coast and across the Rockies today into tonight. The low pressure center will shift east over the Central Plains tonight and into the mid-Mississippi River Valley by Tuesday evening, owing to the southern jet stream. Complicating this surface low will be an additional cold front sagging south from a south- central Canadian low pressure center, which is being activated by the northern jet stream. The split jet will essentially merge over the Midwest tonight into tomorrow, which will expand the precipitation shield across the area tonight through Tuesday. P-type has been the most complicated factor over the past few days with this event, but the overall trend has been to slightly nudge up temperatures little by little each day and model run, culminating in a greater-than-50th percentile forecast in the low temperatures tonight. Also, in addition to the moisture surge accompanying this system will be modest warm air advection in the boundary layer, resulting in a more rain-like p-type pattern for much of the event as it drags on through tomorrow. Thus, the key part is the p-type in the early hours of the event. The SREF and HRRR have been keying in on a wintry mix of freezing rain/snow for west- central into north- central MN with this event, particularly after midnight through midday Tuesday. Model soundings are also indicating a slight enough warm layer off the deck to produce a few hours of potentially prevailing freezing rain for a handful of counties in the northern tier of the WFO MPX coverage area. With a few hundredths of an inch of icing likely, have opted to run with a small winter weather advisory in that portion of the area. South of there, a mainly rain/snow event will unfold but with again lower snow amounts than the previous forecast due to the greater influx of warmer air. Still, up to 1" snow accumulation may develop for the eastern half of the coverage area overnight into Tuesday morning. The p-type will steadily change over to all rain as the day progresses, with the precipitation gradually waning from west to east Tuesday afternoon and evening. A few lingering rain showers are then possible for far eastern and southern portions of the coverage area going into Tuesday night but the vast majority of the coverage area will simply have mostly cloudy skies Tuesday night. After lows tonight drop to the mid 20s in northern and eastern portions of the coverage area and lower 30s in western and southern portions, highs will generally range 35-40 degrees on Tuesday. Could potentially be a couple degrees cooler should some evaporative cooling effects take place, which could nudge up snow amounts by a couple-few tenths of an inch. As the precip ends and the frontal system moves across and departs the area Tuesday night, lows will range from the mid 20s in western MN to the lower 30s in southern MN and western WI. .LONG TERM...(Wednesday through Monday) Issued at 254 PM CST Mon Nov 23 2020 Any lingering light rain or snow showers from left over from the departing storm system will end Wednesday morning. This will set up a relatively quiet period with little to no additional precipitation and temperatures running above normal for late November. Upper level split flow will dominate through the forecast period. Several moisture-starved shortwaves will move through the Upper Midwest. As a result, frontal passages will remain dry and mild air will return behind the exiting troughs. The biggest change from last nights forecast guidance is the shift on the 12z ECMWF and Canadian models. 00z solutions had an amplified trough and jet phasing between the northern and southern streams. This resulted in a storm system that tracked into the Great Lakes keeping the MPX CWA in the cold sector. The 12z solutions now favor the continuation of split flow with no phasing with a closed low over the southern CONUS and a dry frontal passage on Sunday across the upper Great Lakes. Thus, the period will remain dry and mild through the weekend with a potential cooldown for the end of November. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 617 PM CST Mon Nov 23 2020 VFR conditions at the start of the period will give way to MVFR/IFR conditions overnight as a surge of moisture lifts northward. This will bring wintry precipitation across the region, as well as IFR and possibly LIFR ceilings. Winds will be primarily out of the southeast, but eventually become northwest Tuesday evening and overnight. KMSP... Did speed up the start time of the MVFR/IFR conditions as the moisture surge seems to be ahead of schedule. There is a chance for some freezing drizzle, but this looks like more of a snow/rain event for KMSP. Expect IFR conditions for most of the day at KMSP. /OUTLOOK FOR KMSP/ Wed...Lingering MVFR clouds early, then VFR. Wind SW 5-10 kts becoming NW. Thu...VFR. Wind SW 10 kts. Fri...VFR. Wind W 10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...Winter Weather Advisory from 4 AM to 10 AM CST Tuesday for Benton- Douglas-Kanabec-Mille Lacs-Morrison-Todd. WI...None. && $$ SHORT TERM...JPC LONG TERM...BPH AVIATION...JRB