####018006362#### FXUS63 KAPX 190200 AFDAPX Area Forecast Discussion National Weather Service Gaylord MI 1000 PM EDT Thu Apr 18 2024 .KEY MESSAGES... - Rain comes in and moves out tonight. - Colder/breezy Friday with instability showers. - Snow showers possible in some areas late Friday night into Saturday morning. - Rain shower chances next Monday night and Tuesday. && .UPDATE... Issued at 1000 PM EDT Thu Apr 18 2024 Upstream cold front now extends from Western Upper Michigan thru Central Wisconsin into NE Iowa late this evening. Area of light rain continues to develop ahead of this front...now impacting the NW half of Lower Michigan. Expect this area of rain will continues to spread into the rest of our CWA as we head into the overnight hours...and will then exit from west to east by around daybreak. Light rain may end with a brief period of drizzle before ending during the pre-dawn hours. Overnight lows will cool into the upper 30s to lower 40s. && .SHORT TERM /THROUGH SATURDAY/... Pattern Synopsis/Forecast: Amplified large scale pattern across North America and stretching back across the Pacific. One short wave trough moving away from the Great Lakes today with another upper low over Saskatchewan/Manitoba that makes up the eastern portion of a northeast Pacific omega block. Low/mid level cold air push across the northern Plains/midwest/upper Great Lakes...850mb temperatures at or below -4C advecting east across the Dakotas/ Minnesota. Early afternoon surface map shows a broad occluded low over northwest Ontario...cold/occluded front arcs south across western Upper/Wisconsin/eastern Iowa. Widespread clouds northern Michigan at mid afternoon...a combination of diurnally enhanced Sc and Ac advancing in from the southwest along with some mid level radar returns across Wisconsin and central Lower Michigan. Central Canadian upper low will propagate east through Friday... passing north of the Great Lakes but there will be some increasing PV spreading across the forecast area Friday. Associated cold/occluded front crosses Michigan overnight...with deep layer cold air advection in its wake. Primary Forecast Concerns: Rain comes in and moves out tonight: Axis of deeper moisture and large scale forcing/frontogenesis ahead of the cold/occluded front is expected to bring widespread rain chances to northern Michigan tonight. Should be a quick hitting event...window for precipitation looks to be about 6-8 hours though there may be some drizzle on the back end with the front itself. Stability will be weak across northern Michigan but probably not enough for thunder as better instability will be over southern Lower and points south tonight. Highest rainfall potential should be along-east of a CAD-APN line where rainfall totals by Friday morning of 0.25-0.50+ expected (the 0.50+ should be closer to Saginaw Bay). Colder/breezy Friday with instability showers: Behind the occluded front winds will increase from the west and with cold advection/ isentropic downsloping and an increased mixed layer depth should be able to tap into better momentum aloft. Probability for wind gusts to 30 mph in the 40-50 percent range across northern Lower and through the Straits region. Definitely looking at Small Craft Advisories within most if not all nearshore marine zones. As for precipitation chances...cold advection will increase instability across the forecast area but upper level cold pool will settle across Lake Superior allowing for the potential for deeper diurnal convective clouds across eastern Upper and the Straits region Friday afternoon. TQ index values around 17 suggest potential for shallow convective development...some indications of enhanced convergence across eastern Upper won't hurt the cause either. Could see some graupel/snow mixed in given colder mid level temperatures especially in heavier bursts of precipitation. Not sure how far south into northern Lower to pull precip chances with indications of a shallower convective layer/lower inversion heights. For now have kept PoPs north of the M-68 corridor. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... A broad long wave trough covering much of southwest Canada will track slowly to the east over the next couple of days. Meanwhile another trough will drop south out of north central Canada and merge with the first trough and set up shop across northeast Canada for a few days. This is all expected to translate into a period of breezy and mostly below normal temperatures across northern Michigan. In addition, weak disturbances moving through the flow will bring occasional chances for showers Friday night into this weekend. It still looks cold enough for the showers to fall in the form of snow across parts of eastern upper and the higher terrain of northern lower later Friday night into Saturday morning (targeting west northwest favored locals). A light coating of the white stuff would not be a surprise. Lastly, a Pacific trough then brings rain shower chances next Monday night and Tuesday. No precipitation is expected Monday, Wednesday and Thursday. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... A cold front will sweep thru Michigan tonight...producing widespread rain across much of Eastern Upper and Northern Lower Michigan. Rain will end from west to east overnight...with just some lingering scattered shower activity expected across Eastern Upper Michigan for Friday. Prevailing conditions will be low VFR/MVFR for the next 24 hours. Light S/SW winds this evening will become westerly at around 10 kts overnight and will then strengthen to 15 to 25 kts on Friday. && .APX WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory from noon Friday to midnight EDT Friday night for LHZ345>349. Small Craft Advisory from noon Friday to midnight EDT Friday night for LMZ323-341-342-344>346. Small Craft Advisory from noon Friday to 8 PM EDT Saturday for LSZ321. && $$ UPDATE...MLR SHORT TERM...JPB LONG TERM...AJS AVIATION...MLR ####018006821#### FXUS65 KTFX 190202 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 802 PM MDT Thu Apr 18 2024 .SYNOPSIS... A re-enforcing cold front will advance south across the Northern Rockies late tonight and through the morning hours on Friday, bringing another day of well below normal temperatures to Southwest through North Central Montana. In addition to the cool conditions, light snow or flurries are possible on Friday; however, little to no accumulations are expected. Temperatures warm somewhat on Saturday while remaining below normal, with return to near normal temperatures expected by Sunday. && .UPDATE... Minimal amendments were made to the forecast this evening as the latest forecast describes the situation well. Cooler overnight temperatures continue to be expected with the advancement of a southward propagating cold front. Slight chance of light snow showers also remain during the late evening into the overnight period, mainly across the Rocky Mountain Front and portions of Southwest Montana; however, little to no accumulation from these showers are expected. - Pierce && .AVIATION... 520 PM MDT Thu Apr 18 2024 (19/00Z TAF Period) Northwesterly flow aloft will bring periods of isolated to scattered snow showers to portions of Central and Southwest Montana with little impact to surrounding terminals. Periods of gusty winds across many terminals along the Hi-Line and across portions of Central Montana will begin to decrease over the next few hours, returning to a light, occasionally breezy northerly wind. Expect mostly VFR conditions, with lower confidence of MVFR conditions in periods of isolated to scattered snow showers at times. Otherwise, predominately mid-level cloudiness will continue throughout the TAF period for most terminals. - Piece Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 520 PM MDT Thu Apr 18 2024/ Rest of today through tonight...Isolated to scattered snow showers have develop this afternoon over the plains of Central and North Central Montana where earlier clearing allowed surface temperatures to warm sufficiently so that convective temperatures were reached. Additionally, snow showers were also present along the Continental Divide, with additional development expected further south and east across the Central and Southwest Montana mountains through the remainder of the afternoon and evening hours. While snow accumulations will be minimal across most locations given the brevity of the showers, brief periods of reduced visibility to below 1 mile are possible beneath the strongest showers. Where snow showers are more persistent over the higher terrain of the Continental Divide, mainly north of the MT Hwy 200 corridor and south of the US Hwy 2 corridor, snowfall accumulations of 1-3" will be possible through early this evening. While light snow may linger through the overnight hours tonight across portions of Southwest Montana and along the Continental Divide, most locations will see decreasing chances for snow through the evening hours with the loss of heating. Partial clearing over portions of the plains of Central and North Central Montana during the late evening/early morning (Saturday) hours ahead of southward advancing cold front will allow temperatures to cool into the single digits to low teens above zero by Friday morning, with the teens to 20s expected across most valley locations in Southwest and Central Montana. Friday through Friday night...North to northwest flow aloft will prevail over the Northern Rockies through the period as a broad longwave trough, which was draped over most of the CONUS and Canada with an associated closed low over South Central Canada, slowly lifts northeast to over Eastern Canada through Saturday morning. At the surface, a re-enforcing cold front will back in from the north to northeast late tonight through Friday morning as a strong surface high (~1040mb) slides southeast along the Canadian Rockies (Friday morning) to Northeast Montana (Saturday morning). This cold front will bring additional chances for light snow/flurries to areas predominately along and north of the US Hwy 12 corridor on Friday, with widespread low level cloudiness expected over the plains of Central and North Central Montana. These low clouds combined with cold air advecting in across the Northern Rockies will help to keep temperatures in the mid-20s to mid-30s across most plains locations on Friday, with the upper 30s to low 40s expected in the valleys of Southwest and Central Montana. The aforementioned low level clouds will slowly dissipate through Friday evening/night as the low level flow veers to the southeast and south. These clearing skies and light surface winds will allow temperatures to fall into the single digits to teens above zero, with a 20% chance that temperatures fall below zero in the West Yellowstone Area through Saturday morning. - Moldan Saturday through next Thursday... Weak high pressure ridging is forecast to develop over the western United States for much of this period Saturday through Monday, warming temperatures to near seasonal averages. However, a low pressure trough off the Pacific coast of North America is also forecast to eject a shortwave trough over Montana Sunday into Monday, bringing at least a chance of precipitation to much of the area. Right now, though, probabilistic guidance is giving less than a 20 percent chance of 4 inches of snow accumulation in the mountains through this period. Forecast models then indicate that the high pressure ridge will start to amplify Tuesday into Wednesday, which should help warm temperatures to around 10 degrees above normal through mid-week. Mostly dry conditions are also expected on Tuesday, but the low pressure trough is forecast to deepen off the Pacific coast Wednesday into Thursday. This would shift the flow aloft more southwesterly and unsettled, for an increasing chance of showers. - Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 17 35 15 48 / 20 10 10 10 CTB 16 33 17 44 / 10 10 10 0 HLN 23 41 21 54 / 20 10 0 0 BZN 20 42 15 51 / 20 10 0 0 WYS 5 41 4 52 / 20 10 10 0 DLN 19 40 18 53 / 20 10 0 0 HVR 20 38 18 49 / 20 20 10 0 LWT 13 31 15 44 / 20 20 10 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls