####018002161#### FXUS65 KMSO 260825 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 225 AM MDT Fri Apr 26 2024 .DISCUSSION...A large surface low pressure system will be moving onshore of the Pacific NW this morning, transporting moisture over the Northern Rockies from the southwest. Widespread valley rain and high mountain snow showers have developed over north- central Idaho, and will continue to spread across Northern Rockies throughout the day. Late this afternoon, a mid-level circulation is expected to develop over central Idaho and will move east over southwest Montana this evening. Moisture wrapping around the circulation is expected to produce widespread light steady valley rainfall and mountain snow down to elevations of around 6000 feet, with the bulk of the moisture likely lining up with locations along and south of the I-90 corridor. Total valley rainfall amounts through Saturday are expected to be around 0.25", with slightly higher amounts in the mountains. Cool and showery conditions will persist through the day Sunday, with another surface low pressure system projected to bring widespread steady precipitation to region Monday and Wednesday. 70% of ensemble forecast models continue to indicate the first week of May will experience below normal temperatures and above normal precipitation across the Northern Rockies. && .AVIATION...Steady light rainfall has developed over north-central Idaho this morning, and will slowly move northeast over western Montana through the mid-morning hours and this afternoon. All aviation sites across the region will experience periods of steady light rainfall, reducing visibility and lowering ceilings throughout the day. The higher intensity precipitation is expected to be over western Montana between 26/1700-26/2300Z this evening. Snowlevels will be lowering to around 6000 feet overnight through Saturday morning, that could produce periods of light snowfall in areas around KBTM. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$ ####018006969#### FXUS63 KDTX 260827 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 427 AM EDT Fri Apr 26 2024 .KEY MESSAGES... - Dry conditions today with a warming trend lifts temperatures into 60s. - Showers arrive overnight with a chance for a few embedded thunderstorms through Saturday morning. - Breezy southwest winds develop Saturday afternoon with gusts up to 30 mph. - Some additional thunderstorms are possible Saturday evening with an isolated severe storm possible northwest of Metro Detroit. - Additional showers and a few storms are possible Sunday as above normal temperatures continue through mid-week. && .DISCUSSION... Unobstructed cooling and nearly clam winds through the overnight period have sent temperatures into the low-mid 30s across much of the CWA with light ESE flow. High cirrus streamers spilling downstream of a potent shortwave trough closing off over eastern Colorado will begin to interfere with outgoing longwave radiation. This should limit further cooling to just a few more degrees (F) until the diurnal rebound gets underway. Will allow the Frost/Freeze headlines to run their course as dew points remain below freezing. Minor height rises expected through midday as the resident southern stream ridge builds into its northern stream equivalent. Stubborn anticyclone flow then lingers to the east, offering sustained stabilization that temporarily resists top-down saturation processes. Once upper winds back westerly, clouds will work in aloft while the low cloud fraction lags amidst longer duration southeasterly flow. A very broad and highly confluent LLJ featuring impressive latitudinal extent should fold/rotate into southern Lower Michigan this evening providing a shift to southwest flow and aggressive ThetaE convergence. Ultimately, this keeps conditions dry through nearly the entire daylight hours before the sufficient column moistening is achieved. Thermodynamic moderation also gets underway with 850 mb temps increasing by at least 6C by 18Z suggesting highs in the lower 60s, near climatological normals. Cooler readings are anticipated along the coastal communities, downwind of Lake Erie and Lake Huron from on-shore southeasterly flow. By nearly all accounts, showers should hold-off for Southeast Michigan until after 00Z when isentropic ascent commences. This leading arc of showers then transitions to more dynamically forced activity packets of CVA stream through the perturbed mid-level flow with the moistened environment. Forecast soundings reveal some elevated instability above the warm frontal slope, therefore a few rumbles of thunder are possible, late. The mature low exhibits minor pressure rises Saturday as it tracks across the Upper Midwest and merges with the central Canadian trough. Current models suggest a delayed cold FROPA until late Saturday night with a rather dry afternoon. Westerly flow trailing the composite shortwave lends some degree of column drying as lapse rates improve slightly. Did bring PoPs down quite a bit to reflect this trend south of I-69. Main threat for broader coverage of thunderstorms exists across the Tri-Cities INVOF the stalled frontal boundary, higher dewpoints, and SBCAPE. Questions exist regarding afternoon cap erosion per NAM3km/ARW, but a Marginal Risk for severe weather persists. Much warmer conditions arise with highs in the mid- upper 70s in addition to +25 mph gusts. The active pattern continues Sunday as another wave ejects out of the synoptic subtropical jet which reinforces southwesterly ThetaE advection and continued warmth. Several more rounds of showers are possible Saturday night and Sunday with the persistent forced ascent and Gulf-augmented humidity. Some NWP drift now points to more activity occurring over central Lower during the afternoon. Little in the way of cooling mechanisms into Monday as the influence of the departing ridge lingers until Tuesday. High pressure then anchors over the coast of the southern Atlantic which maintains a component of return flow into the midweek timeframe and warmer than normal temperatures through the period. && .MARINE... Strong low pressure moves from the central Plains to the upper Midwest today and then across Lake Superior on Saturday. The strengthening pressure gradient ahead of this system results in southeasterly flow ramping up today, peaking late Friday night into Saturday morning. Wind veers southerly on Saturday with gusts touching gale force during the morning before gradually weakening through the day as much warmer air moves into the region to stabilize flow over the cold lake water. The warm air also fuels thunderstorm potential through Saturday and Saturday night, and possibly even into Sunday as the associated cold front stalls over the region. The front awaits yet another low pressure system moving in from the Plains Sunday into Monday. && .PREV DISCUSSION... Issued at 1155 PM EDT Thu Apr 25 2024 AVIATION... Surface high pressure will remain anchored across the eastern Great Lakes tonight through early Fri morning and will maintain a very light east wind, with the abundant dry air supporting clear skies. An east-southeasterly gradient will increase during the day Friday as the center of the sfc high drifts off the East Coast, with model soundings supportive of wind speeds up around 10 knots. The increased gradient flow will inhibit enhanced lake breeze convergence like today, so the prospects for FEW-SCT diurnal cu is expected to be less. For DTW/D21 Convection...A warm front will approach late Friday night/early Saturday morning. This will support numerous showers toward the end of the TAF period. Increasing instability aloft will also support a chance of thunderstorms, likely embedded within the broader pattern of showers. Chances for thunderstorms will be during the end of the TAF period (08-12Z Sat) and will be around 30 percent. DTW THRESHOLD PROBABILITIES... * Low in thunderstorms overnight Friday into early Saturday morning. * High in ceilings aob 5000 feet overnight Friday into Saturday morning. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Freeze Warning until 8 AM EDT this morning for MIZ047-053-054- 060>062-068-069-075. Frost Advisory until 8 AM EDT this morning for MIZ048-049-055-063- 070-076-082-083. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...KGK MARINE.......BT AVIATION.....SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.