Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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845 FXUS66 KOTX 210429 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 929 PM PDT Fri Sep 20 2024 .SYNOPSIS... Temperatures will be chilly overnight tonight into Sunday morning promoting frost formation for many areas and freezing temperatures in the mountain valleys of northeast Washington. Dry conditions will continue into Sunday. A small chance for light rain mainly over the mountains Sunday night. A ridge of high pressure will deliver above normal temperatures early next week. A more active pattern is expected for the latter half of next week with the potential for breezy conditions, showers, and temperatures returning to near normal. && .DISCUSSION... Tonight through Sunday: The Inland Northwest will be under a dry northwest flow pattern with dew points dropping down into the low 20s and low teens for a few spots. Breezy north to northwest winds bringing in the dry polar continental air mass will relax through the evening hours. There is some moisture aloft moving into the central Washington Cascades that may spread cirrostratus cover from Wenatchee to Moses Lake, but much of the northwest portion of the region is expected to just see thin high cirrus clouds, and it doesn`t appear that these clouds will do much to trap terrestrial radiation to keep surface temperatures from plummeting overnight in the dry air mass. Deeper, sheltered mountain valleys particularly from the Okanogan Highlands over to the Idaho Panhandle should radiate out well overnight as the winds relax. I expect temperatures in these valleys to drop quickly into the 30s and a substantial portion of these valleys dip into the low to mid 30s (e.g. Republic, Metalline Falls, Colville, Chewelah, Deer Park, Newport, Priest River, Athol, Sandpoint, St. Maries, and the Silver Valley). The northern portion of the Upper Columbia Basin, Spokane Area, Coeur d`Alene Area, and Palouse will see the potential for lows in the mid 30s. Chances look favorable for a widespread frost/freeze and anyone with sensitive vegetation should take action to cover plants or bring them indoors to protect them from damage. There is a better potential for cloud cover pushing across the Cascades Saturday and the air mass slightly warmer aloft for Saturday night. Low temperatures by Sunday morning look to be chilly again for the eastern third of the forecast area at least, but looking to be 2-4 degrees warmer than tonight. The freeze warning for the Northeast Mountains covers the overnight period for tonight and Saturday night with frost advisories in the Idaho Panhandle and Palouse in effect for both nights as well. The Okanogan Highlands, Columbia Basin, Spokane Area/Coeur d`Alene Area should see temperatures mild enough overnight Saturday that frost doesn`t look to be a threat. Sunday night through Wednesday: A weak shortwave disturbance pushes across late Sunday. This will bring increasing clouds, but with low levels of the atmosphere so dry, it is unlikely that we will see much precipitation, if any. A warm front pushes across on Monday and this will pump up a high pressure ridge for Tuesday. Temperatures Tuesday into Wednesday will warm up above normal with highs in the upper 70s to low 80s. There continues to be uncertainty with how this ridge will break down. The latest ensembles are now trending toward a quicker break down around Wednesday into Thursday, and bringing through a cold front. Somewhere in the neighborhood of 40% of the ensembles supports this scenario; although, there are varying degrees of strength of the cold front passage. I went ahead and kept what the National Blend of Models (NBM) is forecasting, but a stronger cold front passage would support higher probability for showers and breezy winds. Confidence is increasing that temperatures return to normal at the end of next week, and the break down of the ridge will introduce the possibility for shower chances. /SVH && .AVIATION... 06Z TAFS: Bands of mid and high clouds will move over the region into Saturday with light winds. This will result in continued in VFR conditions. JW FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions through Saturday. JW && .PRELIMINARY POINT TEMPS/POPS... Spokane 37 72 41 74 46 74 / 0 0 0 0 10 0 Coeur d`Alene 38 70 40 71 47 72 / 0 0 0 0 20 0 Pullman 38 68 39 71 45 70 / 0 0 0 0 10 0 Lewiston 45 75 47 77 55 78 / 0 0 0 0 10 0 Colville 33 71 33 72 36 75 / 0 0 0 10 20 0 Sandpoint 35 68 37 68 43 70 / 0 0 0 10 30 0 Kellogg 38 67 42 68 49 68 / 0 0 0 0 30 10 Moses Lake 40 74 43 77 48 77 / 0 0 0 0 0 0 Wenatchee 49 75 52 78 57 78 / 0 0 0 0 0 0 Omak 43 75 47 78 51 79 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Frost Advisory from 2 AM Saturday to 8 AM PDT Sunday for Central Panhandle Mountains-Idaho Palouse-Northern Panhandle. Frost Advisory from 2 AM to 8 AM PDT Saturday for Coeur d`Alene Area. WA...Frost Advisory from 2 AM Saturday to 8 AM PDT Sunday for Washington Palouse. Frost Advisory from 2 AM to 8 AM PDT Saturday for Okanogan Highlands-Spokane Area-Upper Columbia Basin. Freeze Warning from 2 AM Saturday to 8 AM PDT Sunday for Northeast Mountains. && $$