####018005547#### FXHW60 PHFO 031926 CCA AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 859 AM HST Fri May 3 2024 .SYNOPSIS... Breezy trades will become slightly more unstable with pockets of heavier showers possible through the weekend, mainly windward and mauka. A drier moderate trade wind pattern then becomes established by the middle of next week. && .DISCUSSION... Regional satellite shows a closed upper low positioned just SE of 170N/30N. Modest convection, including a few thunderstorms, are noted within its core and beneath the cold pool aloft (-15C at 500mb) several hundred miles NW of the Hawaiian Islands. A shortwave trough wrapping around the southeast periphery of this low is currently enhancing trade wind showers where local moisture is the deepest, mainly over Windward Big Island and Maui. Otherwise, breezy trade winds have settled in and will take the edge off of afternoon heat compared the last several days as showers focus over windward and mauka zones in routine fashion. Trades will then acquire a decreasingly stable character as the aforementioned upper low opens up and shears east along the northern periphery of the subtropical jet. The inversion is modeled to weaken and lift by a few thousand feet which will increase the depth of trade wind showers as they advance across the area. This will facilitate slightly greater rain rates and increase leeward penetration of showers. Waves of forcing rotating around the low will be responsible for periodically increasing shower coverage Saturday night through early next week. During this time, the cold pool aloft will move directly overhead and is modeled to moderate to around -11C at 500mb. Lapse rates will still be adequate for pockets of deep convection to develop Sunday night through Monday night, mainly during the overnight periods. Isolated thunderstorms cannot be ruled out during this period, but confidence at this stage is too low to warrant explicit inclusion in the forecast. Meanwhile, a separate thunderstorm threat may manifest over the Big Island where a plume of steep lapse rates on the order of 7C/km is modeled to extend northeastward over the eastern end of the state. This will contribute to an increased probability of pockets of heavy showers and/or isolated thunderstorms Sunday and Monday afternoon, particularly as the upper jet provides maximum venting aloft on Sunday followed by the upper wave itself pivoting through on Monday. Confidence at this stage once again falls short of inclusion in the forecast but will be given consideration in future forecast cycles. Pressure falls over a broad swath of the Central Pacific will then ease the gradient leading to a drier moderate trade wind pattern by the middle of next week. && .AVIATION... Breezy easterly trades will continue today as high pressure builds in from the NE and pushes the surface trough NW of Kauai further away from the state. Moisture riding in on the trades will focus clouds and showers over windward and mauka areas, with the greatest shower activity during the late night and early morning hours. A few showers may spill over to leeward areas at times. VFR conditions will generally prevail, but MVFR conditions will be possible in any heavier showers that develop. AIRMET Sierra is in effect for tempo mountain obscuration for windward and mauka portions of the island chain. This AIRMET will continue for a few more hours this morning and may be needed again late tonight. AIRMET Tango is in effect for mod turb below 080 downwind of island terrain. Conditions are borderline, but should continue through the day. AMD NOT SKED in for Midway due to missing wind speed and direction && .MARINE... Consolidating high pressure far north-northeast of the state will produce fresh to strong trade winds across Hawaiian waters for the next several days. These stronger trades may drop slightly early next week as the high begins to move farther to the northeast. An advanced scatterometer (ASCAT) pass last night showed Small Craft Advisory (SCA) level winds across most coastal zones already, and these will continue through the weekend. As a result, a SCA remains in effect for all Hawaiian waters through early Monday morning. Tiny surf will persist along north and west facing shores through much of today. Forerunners of a long period northwest swell are expected to fill in later this afternoon and peak Saturday, bringing small surf along north and west facing shores. Another small, long period northwest swell will fill in late Sunday, maintaining small surf along north and west facing shores into early next week. Small background south swells will continue into Saturday, providing tiny surf for south facing shores. Forerunners of a small, long period south swell may arrive Saturday afternoon with a slow onset through Sunday providing a boost in surf along south facing shores into early next week. Rough and choppy surf along east facing shores will increase slightly on Saturday and hold into early next week as strong trades persist. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Monday for all Hawaiian waters- && $$ DISCUSSION...JVC AVIATION...Farris MARINE...Vaughan ####018004150#### FXUS63 KARX 031926 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 226 PM CDT Fri May 3 2024 .KEY MESSAGES... - Showers and scattered storms are expected mainly Saturday. Rainfall amounts of up to a half of an inch from the showers or storms. - Active pattern develops next week with periodic showers and storms through much of next week. Timing of convection into region remains an issue and will have impacts on the severe potential across the forecast area. && .DISCUSSION... Issued at 226 PM CDT Fri May 3 2024 Today through Saturday: While quiet weather is in store for the rest of the day, guidance continues to support a shortwave moving through the area on Saturday. Accompanying this wave will be a 30 to 40kt 850mb jet that will help to increase the moisture transport. PWATs will increase into the 1 to 1.3 inch range. Recent guidance continues to show some instability moving further north, as shown by general consensus of 250 to 500J/kg of SBCAPE. The highest instability continues to be in southern Wisconsin. Despite this instability, it is not enough to promote any severe weather, even with the high amounts of shear, 30 to 50kts of 0-6km bulk shear. This means that thunderstorms will be possible as the band of precipitation moves through the morning and early afternoon on Saturday. Sunday into Monday Shortwave ridge builds into the Upper Great Lakes Region Sunday into Monday. Subsidence underneath ridge will allow for mainly dry weather across the forecast area both days. With light winds near the surface...clear skies and an inversion developing over the forecast area Saturday night/Sunday morning. There is the possibility of fog formation across parts of the area...mainly in low lying areas/river valleys. However...if northwest winds stay up enough...fog may not form. At this time...have left mention of fog out of the forecast. Warmer airmass advects into the region Sunday into Monday...as 925mb temperatures warm from around plus 10 degrees celsius Sunday to near plus 14 degrees celsius by 00z Tuesday. High temperatures will be mainly in the 60s Sunday and warming into the upper 60s to middle 70s Monday. Monday night through Friday Main forecast concerns from Monday night through Friday continues to be shower/storm chances through much of the forecast period. Upper level closed low slowly moves over the Northern Plains States and weakens during the forecast period. Latest ensembles/deterministic models continue to show differences in timing of the upper level closed low/impulses rotating around the closed upper level low into the Upper Mississippi River Valley. Confidence in timing of convection and any severe potential with the storms remains low. The latest GFS/ECMWF continue to indicate vertical motion/moisture convergence with the closed upper level low/impulses. This will produce periodic showers/storms through much of the forecast period...Monday night into Friday. Temperatures will remain near or slightly above normal with highs generally in the lower 60s to middle 70s through the forecast period. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1239 PM CDT Fri May 3 2024 Light southwesterly winds expected through the evening, then shifting to southeasterly winds for the overnight period. A line of showers will move through Saturday mid-morning and early afternoon across the area. There is around a 30% chance of thunder to occur within this line, so thunderstorms can not be ruled out. Lower flight categories are expected, especially MVFR conditions. IFR conditions will be possible, as there is between a 20 and 40% chance of IFR CIGS to occur during the morning and afternoon. The wind will shift to the northwest across the area during the afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...DTJ AVIATION...Cecava