####018004328#### FXUS63 KGRR 040301 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 1101 PM EDT Fri May 3 2024 .KEY MESSAGES... - Increasing Chance for Showers/Storms Later Saturday into Saturday night - Dry end of the weekend - Many chances for rain next week && .UPDATE... Issued at 1101 PM EDT Fri May 3 2024 Nighttime microphysics imagery shows low clouds beginning to fill in across Southeast Lower Michigan this evening. Observations confirm the low clouds with bases below 1,000 feet at several sites. This stratus should expand and roll into Southwest Lower Michigan from the east overnight as easterly winds advect the clouds in. So, quite a bit of the area will be mostly cloudy at daybreak. Some fog is expected as well, especially near and north of I-96. Visibilities below 1 mile are expected. Maximum extent of the stratus and fog should be around 700am. We expect clearing to take place by midday. && .DISCUSSION... Issued at 231 PM EDT Fri May 3 2024 - Increasing Chance for Showers/Storms Later Saturday into Saturday night Southerly winds ahead of an approaching cold front will draw up moisture from the south Saturday into Saturday night. Instability increases as well later Saturday afternoon into Saturday night, but overall remains weak. Aloft some upper level divergence is seen Saturday night over the CWA so that may enhance the lift. Thus the combination of moisture, lift and instability will likely lead to showers and a few storms. Ensemble QPF values, while low, have been trending up with the precipitation for this period. - Dry end of the weekend High pressure over the upper Mississippi Valley will produce plenty of sunshine Sunday. Highs will climb to a couple of degree either side of 70. - Many chances for rain next week The persistent upper trough over the western US is progd to cut off over the northern High Plains during the middle of the week. The result will be several short waves that move in our direction and bring chances for showers and storms. Tuesday night through Wednesday night will be a time frame that will see increased chances for precipitation. An occluded front will lift north toward Lower MI Tuesday afternoon and this will produce some showers/storms. Present indications are that the strongest instability will remain south of the state. However, that could changed this far out. SPC has already highlighted areas to the southwest of the state for the potential of severe storms. Another chance of showers/storms will come Thursday and Thursday night, when the surface low over the northern Plains moves east. Accompanying short waves and a feed of moisture rich air from the south will spur convective development during this time. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 757 PM EDT Fri May 3 2024 A combination of lingering low level moisture that will not decrease substantially behind this afternoon's cold frontal passage and a flow off of Lake Huron will produce stratus and fog tonight. We will be VFR through any flights at the TAF sites through 05Z or so. After 05Z, the stratus and fog will be making a push into Southwest Lower Michigan from the east. MVFR and IFR ceilings will develop at LAN and JXN around 06Z and overspread GRR/BTL and AZO by 09Z. The stratus will press into MKG by 11Z. The lowest conditions, IFR and potentially LIFR will occur between 09Z and 13Z. Low clouds will lift to VFR through the daylight hours of the Saturday morning (12Z-16Z). VFR weather is expected Saturday afternoon. Winds will become east tonight and gradually become southeast and south on Saturday. && .MARINE... Issued at 231 PM EDT Fri May 3 2024 Southerly flow will be on the increase Saturday into Saturday night as a front moves in from the west. This will be warm air advection and overall the values are expected to remain under 20 knots. Thus we don't plan on needing headlines a this time. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ UPDATE...Duke DISCUSSION...MJS/04 AVIATION...Duke MARINE...MJS ####018006850#### FXUS65 KBOI 040304 AFDBOI Area Forecast Discussion National Weather Service Boise ID 904 PM MDT Fri May 3 2024 .DISCUSSION... Tonight, the forecast area will experience warm and dry conditions as an upper-level ridge persists overhead. Late tonight, this ridge will shift eastward as the next upper-level low approaches from the west. By Saturday, a well-developed upper-level low pressure system will impact the region, bringing initially windy conditions followed by heavy rainfall. Winds will pick up after sunrise on Saturday, starting from the east and then shifting to the northwest behind a cold front in the afternoon and evening. Along the I-84 corridor from Twin Falls to Baker City, and across higher open terrain in southeast Oregon, sustained winds of 25-35 mph with gusts of 40-50 mph are expected ahead of the front, as detailed in the current wind advisory. Furthermore, several high-resolution models indicate the potential for stronger thunderstorms ahead of the cold front across south- central Idaho on Saturday afternoon. With forecasted surface temperatures in the low 70s, along with 50 knots of shear and 200 J/kg of CAPE, there could be a few stronger thunderstorms from the Idaho/Nevada border through the Upper Treasure Valley and Western Magic Valley. A substantial precipitation band will form along the cold front preceding the low, spreading from southeast Oregon early Saturday to southwest Idaho by late afternoon. Models are in good agreement with a 60-80% probability of receiving 0.50 inches or more of liquid across much of the area, and a 20-40% chance of exceeding 1.00 inch. Snow levels are expected to remain elevated above 6500 feet, then falling to around 4500 feet by Sunday afternoon. The current forecast captures the precipitation well, and thunderstorms have been added to the forecast for Saturday afternoon. An update will be released shortly. && .AVIATION...VFR tonight. Widespread rain moving into SE OR by late Saturday morning and into SW ID late afternoon. Isolated thunderstorms developing across SW ID Saturday afternoon and early evening. MVFR/IFR conditions and mountain obscuration in precipitation. Snow levels 7-9kft MSL, lowering to 3-4kft SE OR and 4-6kft SW ID by Sunday morning. Areas of LLWS developing overnight into Saturday morning, especially across the Treasure Valley and portions of SE OR, with winds S-SE 35-45 kt at 2000 ft AGL. Surface winds: S-SE 10-25 kt, with gusts 25-40 kt on Saturday. Winds becoming W-NW 10-20 kt Saturday evening behind a cold front. Winds aloft at 10kft MSL: S 20-35 kt. KBOI...Increasing mid to high clouds overnight. Rain developing late Saturday afternoon and continuing overnight. MVFR conditions developing in rain. LLWS tonight until surface winds increase. SE surface winds increasing tonight into Saturday to 15-25 kt with gusts 25-35 kt. Winds becoming NW 10-15 kt Saturday evening. Sunday Outlook...Showers continuing on Sunday, especially in the mountains. Areas of MVFR/IFR conditions and mountain obscuration. Snow levels 3-6kft, lowest in SE Oregon in the morning. Surface winds: W 10-20 kt with gusts 20-30 kt. && .PREV DISCUSSION... SHORT TERM...Tonight through Sunday night...Dry, warmer, and increasingly windy weather overnight and Saturday ahead of an approaching north Pacific cold front. Southeast through southwest winds will increase in southern CWA zones Saturday, reaching 30 mph with gusts to 45 mph, enough for a Wind Advisory in the Upper Treasure Valley and western Magic Valley, and the southern half of Harney County. These winds will help boost temps to near 70 degrees Saturday in the southern Idaho valleys, and 60s in the rest of Idaho, but only 50s and 60s in Oregon as rain will begin there around midday. A deep upper low in the north Pacific will come inland along the OR/CA border late Saturday then due east along the southern OR border Saturday night and southern Idaho border Sunday. This is an ideal track for pcpn in our CWA. The rain will be moderate to heavy late Saturday through Saturday night as the cold front moves eastward across our CWA. Totals will be .50 to 1.25 inch in the mountains, and .30 to 60 inch in the valleys. Snow level will drop sharply behind the cold front all the way to valley floors in Oregon, and 3500 to 4200 feet MSL in western Idaho Sunday morning. But by then most of the pcpn will be ending so snow totals will only be a couple inches, except above 7000 feet where a foot may fall. Behind the cold front Sunday's high temps will be some 20 degrees lower than on Saturday, only in the 30s and 40s in the mountains and 40s to lower 50s in the valleys. Sunday will also be windy but not as windy as Saturday, and from the west or northwest. Lighter rain and snow showers will continue Sunday night as moisture wraps around the eastward-moving upper low. Thunderstorms were taken out of the forecast, except for a 15 to 20 percent chance in southern Twin Falls County Sunday afternoon. LONG TERM...Monday through Friday...Northwest flow aloft will prevail as a deep low moves eastward out of the area. Embedded in the flow, another trough will move into the area late Monday and early Tuesday. As this trough moves into already moist and cold air, it will extend the chances (50-70%) of precip through the early parts of the long term. With snow levels still between 5000-6000 ft MSL, a chance for mtn valley mixed precip will exist, while mtns continue to favor snow. At the same time, Monday afternoon instability supports a slight chance of thunderstorms in the W-Central Mtns of Idaho and the ID/NV border. Precipitation chances will taper off between Tuesday and Wednesday as the trough exits the area, but a slight chance for showers will remain over central Idaho through Thursday morning. Models continue to agree on a period of calmer weather kicking off on Thursday, as a ridge of high pressure builds north of our area. The exact position of the high varies, but the forecast remains the same: warmer, drier, calmer by the end of next week. Temps will rise from 10-15 degrees below normal on Tuesday to near normal on Thursday/Friday. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...Wind Advisory from 9 AM to 6 PM MDT Saturday IDZ014-016. OR...Wind Advisory from 8 AM to 5 PM PDT Saturday ORZ061. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...JDS AVIATION.....ST SHORT TERM...LC LONG TERM....JM