Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/10/20

Area Forecast Discussion
National Weather Service Bismarck ND
948 PM CDT Fri Oct 9 2020 .UPDATE... Issued at 948 PM CDT Fri Oct 9 2020 Temperatures along the Canadian border in closest proximity to the surface ridge axis are already falling a bit faster than had been forecast, so we lowered forecast lows a bit area-wide, but mainly in the north central where some upper 20s F are being advertised closest to the Canadian border. Otherwise, RAP soundings through its 01 UTC cycle along with the new, 00 UTC NAM suggest winds in western ND could indeed be a bit stronger tomorrow, which could tip the scales toward potential Red Flag Conditions. We`ll defer any action on a potential headline until we`re able to digest the full 00 UTC model suite though, and make a decision on that with the ~4 am CDT forecast release, as we already have near-critical fire weather conditions mentioned in our forecast messaging. UPDATE Issued at 639 PM CDT Fri Oct 9 2020 Only minor changes were made with this update, mainly to account for observational trends, including a period of high cloud cover crossing the area this evening in association with a weak short- wave trough noted on water vapor imagery. Otherwise, light winds and a dry boundary layer are on track to yield a cool night with surface ridging building into central and eastern ND. Our official forecast lows are near the 10th percentile of model guidance, and thus on the cool side of the solution envelope, but the favorable radiational cooling conditions and recent tendency for guidance to be too warm with its forecast lows both support that strategy. && .SHORT TERM...(This evening through Saturday) Issued at 201 PM CDT Fri Oct 9 2020 Main forecast issue in the short term period will be fire weather issues on Saturday afternoon. Mostly sunny and a little breezy this afternoon behind and exiting cold front. High pressure already pushing into the west will allow for a quick drop off in winds this evening and an overall seasonable to cool night. Temperatures will range from the low to mid 40s southwest to the lower 30s around the Turtle mountains, closest to the surface high Saturday morning. Will get into more detail about fire weather in the fire weather discussion below, but look for sunny and breezy to windy conditions on Saturday with highs in the lower 60s around the Turtle Mountains, to the upper 70s in the far west. An upper level trough moving onto the Pacific Northwest coast will induce lee cyclogenesis in the northern U.S. and Canadian Rockies Saturday with an increasing southerly flow over the Dakotas. .LONG TERM...(Saturday night through Friday) Issued at 201 PM CDT Fri Oct 9 2020 The main forecast issue in the long term period will be winds and fire weather issues. Breezy conditions expected through the period with little in the way of significant precipitation, and an overall cooling trend through the work week. A strong low level jet tracks west to east across the forecast area Saturday night. Were this summertime and if we had some moisture around maybe we would get some convection along the nose of the 850 mb jet, but right now it looks too dry. It should allow for a mild and breezy overnight period with lows in the 50s across much of the forecast area. On Sunday, the aforementioned (Short Term) upper low lifts from southeast Alberta through southern Saskatchewan. Western and central North Dakota will remain in the warm and dry sector of this system. Although the system is strong, we remain quite dry, so the main precipitation chances will be Sunday afternoon/early evening, behind the surface cold front, associated with the forcing from the mid level trough. It looks like it will be too dry for convection ahead of the cold front, until it reaches far eastern portions of South Dakota and southeast North Dakota. It will be another breezy to windy day on Sunday with a period of strong winds directly behind the cold front that moves through, but with strongest winds in the late west Sunday afternoon. See fire weather discussion below for details. Monday will be another dry and windy day as the upper low lifts northeast through Manitoba. We remain in a northwest upper flow pattern through much of the work week with occasional impulses bringing meager precipitation chances. At this time there isn`t a strong enough signal to pinpoint any one period, but would not be surprised to see a couple chances of light precipitation during the work week. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 948 PM CDT Fri Oct 9 2020 VFR conditions are forecast through the 00 UTC TAF cycle. Light winds tonight will become southeast by daybreak, then increase, with gusts of 30-35 kt common on Saturday. Low-level wind shear is possible late tonight and early Saturday morning in the west prior to surface winds increasing, especially at KXWA. && .FIRE WEATHER... Issued at 948 PM CDT Fri Oct 9 2020 Near critical fire weather conditions are expected Saturday afternoon, and possibly again Sunday afternoon in western North Dakota. Strong southerly winds are expected to develop Saturday morning over western North Dakota, and slowly shift into central North Dakota during the afternoon. Sustained winds around 20 to 25 mph are expected over western North Dakota Saturday afternoon. Due to limited moisture, afternoon humidities are expected to drop to 15 to 25 percent. A limiting factor is that the lowest humidities will be in the far west, in the mid to late afternoon, while the strongest winds will be moving out of the far west during this same time. The most recently-arriving data this evening suggests winds could be a bit stronger than forecast, and we will further evaluate the potential need for a Red Flag Warning with the morning forecast issuance. On Sunday, it will be much cooler over the west, but winds will be stronger. There may be a period of time in the late afternoon where sustained wind speeds are around 30 mph with humidities around 30 percent, yielding near critical fire weather conditions. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...CJS SHORT TERM...TWH LONG TERM...TWH AVIATION...CJS FIRE WEATHER...TWH/CJS
Area Forecast Discussion
National Weather Service Grand Rapids MI
708 PM EDT Fri Oct 9 2020 LATEST UPDATE... Update/Aviation .SYNOPSIS... Issued at 300 PM EDT Fri Oct 9 2020 - Mild and likely dry weekend - Occasional rain chances next week && .UPDATE... Issued at 708 PM EDT Fri Oct 9 2020 I have increased the cloud cover Saturday morning to overcast and added some patchy light rain/drizzle to our forecast. This impacts ares south of Route 20 more so than area north of there. Areas near I-94 will be most impacted by this as the clouds will linger there until after dark. The threat of rain is highest near I-94 too. The latest run of the HRRR (21z) has between .03 and 0.08" of rain in the I-69 area Saturday afternoon. Looking at just about all of the latest hi-resolution model sounding forecasts for Saturday morning I seen a strong frontal inversion near 5000 ft agl. The air below that is nearly saturated most of the day until the drier and cooler air moves in from the north. Typically if the air temperature in the colder air is below the dew point of the air in front of the front you get low clouds behind the front. This rule works amazingly well. I will admit this is close, dew points should be in the lower to mid 60s ahead of the front and air temperatures behind the front should be in the mid 60s to near 70. Since the HREF really likes this idea and it fits most of the other considerations, I do believe we will see low clouds behind the front with some patchy drizzle. && .DISCUSSION...(This evening through next Friday) Issued at 300 PM EDT Fri Oct 9 2020 -- Mild and likely dry weekend -- At least scattered cloud cover should move in tonight with 900-800 mb moisture transport. Expecting it to stay much more mild tonight versus last night, as pressure gradient winds at the surface won`t cease and dewpoints in the 50s are poised to move in. An EML from 700-550 mb tonight has steep lapse rates, resulting in several hundred J/kg of MUCAPE tonight from the moist parcels at 850 mb, however, the base of the EML is too warm and should serve as a strong enough cap to prevent thunderstorm development overnight into Saturday morning. As a weak surface cold front slips through the area on Saturday, 850 moisture lingering under the weakening cap (but also weakening lapse rates) may be just enough to touch off weak convection during the afternoon in southern to southeast Michigan. Any sprinkles or showers that develop would quickly move east. We`ll mention a chance of a sprinkle around Lansing, Jackson, and Battle Creek. The moisture from Hurricane Delta looks more likely to move up the Ohio River valley on Sunday and stay away from Michigan. -- Occasional rain chances next week -- A robust jet streak moves into the northwest CONUS early next week and a trough sharpens in the left-exit region over the northern Plains. This trough may go a bit more negative-tilt as it approaches Michigan, but instability is in question for Monday. Ensembles favor a quick round of rain totaling between a tenth and half inch, perhaps as a cold frontal rain band. With quite a bit of unidirectional shear in place for Monday afternoon, the amount and depth of any instability will be key to watch for. Ensemble spread increases after Tuesday, presumably due to differing solutions for how the cyclonic gyre develops in central Canada and moves later in the week. Shortwaves moving through the flow in the northern CONUS may bring us an occasional chance of showers during the week. By late in the week, there`s some ensemble signal for the western North American ridge to rebuild as the Canadian low drifts toward southern Hudson Bay, which would favor a cooling trend here. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 708 PM EDT Fri Oct 9 2020 Our long string of days in a row with nearly clear skies is about to come to an end. A cold front will drop south into southern Lower Michigan during the mid to late morning hours. Once the front comes through expect MVFR cigs to last for about 6 hours behind the front. After that enough dry air should follow the front to clear the clouds out. It also looks like there will be some drizzle or light rain behind the front, but at this point it does not look like enough to impact visibilities that much. However, in the I-69 area (LAN/JXN) some our latest HRRR model runs would indicate otherwise. They are giving around 0.05" of precipitation Saturday afternoon. If that happens and it is light rain or drizzle, the visibility would be impacted. For now I put VCSH and will call that good. Expect low level wind shear most of the night into Saturday morning until the front comes through. Winds of 40 to 50 knots will get as close at 1500 above the ground tonight. && .MARINE... Issued at 300 PM EDT Fri Oct 9 2020 Winds and waves hazardous to small craft will continue into Saturday morning, as southwest winds veer from the west and then north. Waves should still be choppy south of Whitehall Saturday afternoon, but we anticipate ending the small craft advisory there and south, while extending the advisory north of Whitehall into Saturday evening, as waves near Big and Little Sable Points will still be 3-5 feet. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Small Craft Advisory until 11 AM EDT Saturday for LMZ844>849. && $$ UPDATE...WDM SYNOPSIS...CAS DISCUSSION...CAS AVIATION...WDM MARINE...CAS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
838 PM CDT Fri Oct 9 2020 .UPDATE... 838 PM CDT No significant change to forecast tonight. Winds have decoupled a bit more strongly than expected with sunset this evening, though 1-min ASOS obs still indicating sporadic gusts into the 20-25 mph range. Otherwise, an occasionally breezy and mild early October night is in store, with overnight lows in the 60-65 degree range not too far below our average high temps for this time of year. Cold frontal passage on Saturday still looks the same, with a sharp drop in temperatures near the lake as winds turn northeasterly by early afternoon. Forecast appears to be in good shape in depicting these trends. Ratzer && .SHORT TERM... 342 PM CDT Through Saturday night... Gusty winds will continue through the late afternoon today before easing somewhat by the evening hours with the loss of deep diurnal mixing. Guidance varies somewhat on the degree of boundary layer decoupling overnight tonight, but with the surface pressure gradient not really expected to loosen up much until dawn and with 20+ kt flow at under 500 ft AGL, we could still see sustained southwesterly winds of around 10 mph with sporadic higher gusts which will help keep overnight lows in the upper 50s/low 60s and possibly even mid 60s within the Chicago metro. Any lingering ground-level smoke and/or crop dust from central Illinois should mix out and/or move out of the area by this evening, but the elevated smoke from western wildfires is likely to persist into tomorrow morning, albeit at lower concentrations than seen today. Primary focus for Saturday will be on a lake-enhanced back door cold front that will drop southward through the area tomorrow afternoon, which will play a role in dictating tomorrow`s high temperatures. Remain fairly confident about locations south of I-80 reaching high temperatures at or close to 80 degrees again, but most areas north of I-80 will likely only reach highs in the low/mid 70s at best prior to the front coming through and dropping temperatures by around 15 degrees or so in many areas prior to sunset. With increasing likelihood of a stratus deck developing along and slightly ahead of this front, in addition to model guidance trending towards a slightly faster progression of the front, wouldn`t be surprised if some locations north of I-80 ended up with lower high temps than currently forecasted. With some models suggesting saturated or nearly saturated atmospheric profiles through the entirety of the 850-750 mb column, can`t rule out the possibility of some drizzle or light showers along the front either, but with a fairly dry sfc-900 mb layer, have opted to continue with a dry forecast for now. Ogorek && .LONG TERM... 342 PM CDT Sunday through Friday... There are no significant weather impact concerns in the long term period. The main items of note include cloud cover trends on Sunday, rain/showers and maybe isolated thunder on Monday, and likelihood of a more significant cool down later next week. Finally, in what looks to be another shortwave train next week, there will be several periods of breezy to potentially windy conditions. Any lingering low clouds that are expected to drift southward behind the back door cold front passage on Saturday, have a signal in several guidance members to either be advected and/or redevelop back northwestward late Saturday night into Sunday morning. With the much lower sun angle, this possibility casts some uncertainty on Sunday`s high temperatures, especially with north and northeastward extent. Suspect that the NAM as it typically is, is too aggressive with the sharpness of the inversion and moisture depth under the inversion. Therefore think that the clouds will eventually erode, with lowest confidence north and northeast as mention, along with doubting there will be any drizzle. Finally, steady easterly flow from the cooling Lake Michigan waters will keep conditions cooler along the Illinois shore and several miles inland. Lowered the going forecast highs to the north of I-80, especially IL shore and inland over far northeast Illinois into the mid to upper 60s. The best chance for temperatures into the upper 70s and even flirting with 80 would be across the far interior CWA. Sunday night will feature a steady southeasterly breeze in advance of Monday`s sharp cold front passage. This will keep temperatures propped up to primarily upper 50s-low 60s, well above normal for mid October. The stout short-wave expected to bring a period of rain/showers on Monday will primarily be anafrontal (post-frontal) and partially driven by frontogenesis, so think that most of the rain will be after daybreak Monday, and track relatively quickly from west-northwest to east-southeast through the day. With good run to run consistency on this feature, have increased PoPs into the likely range. Plume of relatively steep lapse rates associated with the narrow belt of strongest forcing could support some widely isolated embedded thunderstorms. The rain should end quickly from west to east from the afternoon through sunset. Given the quick hitting nature of the rain/showers, amounts should stay in check at generally no more than 1/4". The other item of note with Monday`s forecast is the sharp wind shift to gusty northwest winds behind the front that will bring falling temperatures through the afternoon after mid day/early afternoon highs in the upper 60s to lower 70s (mid 70s far southeast). There may be a brief window right behind the front where wind gusts could be up to or over 30 mph. Tuesday should feature near seasonable temperatures ahead of the next wave and yet another cold front. No precip mention yet, but some light showers can`t be ruled out. The strongest cold front passages of the week will occur Wednesday night into Thursday as a long wave trough sets up over the north central CONUS from a strong upper low over Hudson Bay. Wednesday could be a bit more of a warm-up than depicted in the official forecast in the warm advection ahead of the front, then Thursday will cool down to the upper 50s to lower 60s. A secondary cold front/reinforcing cold shot Thursday PM will then bring unseasonably cool conditions to close out the work week, with highs only in the 50s if not cooler on Friday as 850 mb temps plunge to below 0 Celsius. As mentioned in the intro, the fast flow pattern with multiple short-waves will bring multiple periods of breezy/gusty winds, each of which that could have gusts up to 30-35 mph and possibly occasionally stronger. Castro && .AVIATION... For the 00Z TAFs... Aviation forecast concerns: * Breezy southwest winds persist tonight. * LLWS potential overnight if surface winds decouple more strongly than expected. * Surface cold front moves through terminals around midday Saturday. Shift to northeast winds with some gustiness persisting into the evening. * Potential for some patchy MVFR ceilings behind the front Saturday afternoon. Fairly deep surface low pressure will pass north of Lake Superior this evening, with a cold front trailing across the upper Mississippi Valley eventually moving into the forecast area on Saturday. In the near term, breezy south-southwest winds are diminishing some with the approach of sunset, though substantial flow above the boundary layer is expected to continue to produce sporadic gusts into the overnight hours. Should the boundary layer decouple more strongly than expected, stronger winds of 40-45 kt in the 1000-2000 foot AGL layer would present an LLWS concern. Considerable amount of wildfire smoke (as depicted in HRRR model dispersion forecasts) will linger and make for some hazy skies overnight, though it appears that surface visibility will remain greater than 6SM. Otherwise dry air mass will produce only patchy high clouds at times. The surface pressure gradient will weaken late tonight into Saturday morning as the surface cold frontal trough approaches. Several models (HRRR/RAP and ECMWF) continue to support a little earlier frontal passage around midday. Winds are expected to shift to the northeast with some gustiness by early afternoon. Air mass north of the cold front is fairly dry, as indicated by mid-30s to mid 40s surface dew points, which decreases confidence in the development of substantial ceilings below 2500 foot behind the front. NAM-based guidance continues to suggest the potential for some lower MVFR stratus/stratocu development but it tends to have a moist-bias in the boundary layer and suspect it`s over forecasting the magnitude of the low cloud threat. Thus have gone a little more optimistic with ceilings behind the front Saturday afternoon. Cold fropa should clear out any remaining smoky haze. Surface high pressure then builds southeast across Ontario and the northern Great Lakes into Saturday evening. The gradient is forecast to tighten a bit between the southern periphery of the high, and the remnant circulation of hurricane Delta to the south. It is likely that northeast winds will remain gusty near 20 kt at times (and perhaps even increase a bit) into Saturday evening. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...IL nearshore waters until 1 AM Saturday. Small Craft Advisory...IN nearshore waters until 4 AM Saturday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at: