A cool upper-level trough over the Inland Northwest coupled with an inverted surface trough axis over the northern mountains of Washington focused numerous convective snow showers through the day. This led to light to moderate snow accumulations across the Okanogan Highlands.
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The episode as NWS OTX wrote it up.
A cool upper-level trough over the Inland Northwest coupled with an inverted surface trough axis over the northern mountains of Washington focused numerous convective snow showers through the day. This led to light to moderate snow accumulations across the Okanogan Highlands.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Spokane, WA wrote its last area forecast discussion before the first event at Apr 8, 3:30 AM PST, 6 hours 20 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 430 AM PDT Mon Apr 8 2013 .SYNOPSIS... Cool and showery weather will occur through today...with further snow accumulations likely for the Cascade passes. The next break in the active weather pattern will be on Tuesday but active...showery and breezy weather will return on Wednesday. A progressive weather regime with more showery storm systems are expected later in the week through next weekend. && .DISCUSSION... Today through Tuesday...A deep upper level trough is digging into the Western United States...with the dynamic trough base energy focused over the Great Basin today. The forecast area is left under the extreme northern area of this trough...in sort of a dead zone where an old surface low which tracked into the region yesterday is now stationary over the northern mountain zones and slowly dieing. Through today and this evening this expiring low pressure and some amorphous orphaned vorticity centers will serve as a focusing mechanism for scattered to numerous showers over much of the forecast area...not as dense or prevalent as yesterday's activity but none-the-less present. During the morning just about any part of the forecast area will be subject to a rain or non-accumulating snow shower...but by afternoon the main activity will be valley rain and mountain snow showers largely confined to the far eastern Columbia Basin and the mountains north and east of the basin. the presence of the weakening surface low creates a split in the low level wind/pressure field today...with westerly winds over the deep basin and Cascades lee...and easterly flow over the east. Some weak seepage of a continental Canadian Polar air mass through the Rockies and down the Purcell Trench today will keep high temperatures from reaching seasonal normals today over the east. Thus overall today looks like a cool and showery day with some sunbreaks possible between the convective towers. While there is some residual instability aloft and possibly some weak SB CAPE especially if sunbreaks occur...the weakening nature of any dynamics preclude the mention of any thunderstorms this afternoon and evening. Tonight and Tuesday the deep upper trough pinches off into a Great Basin closed low leaving the forecast area in a quiet weather regime under a flop-over ridge aloft. No significant weather is expected tonight and Tuesday other than patchy morning valley fog and increasing high clouds filtering the sun on Tuesday. /Fugazzi Tuesday night to Saturday: The Inland Northwest will be in progressive pattern, with the occasional precipitation threat and breezy conditions. There are lingering inconsistencies from model run to model run regarding the system timing. Yet mean model solutions point to Wednesday and Friday night/Saturday as wetter periods as more organized systems move through. Mild temperatures around mid-week cool to slightly below normal by the week's end as the jet stream shifts south. Tuesday night a warm front moves into the region. Moisture spilling over it leads to thickening clouds for much of the region, with precipitation chances increasing across the Cascades and northeast mountains. Yet dry weather will continue for the majority of the Inland Northwest. Then Wednesday (into Wednesday night) deepening low pressure tracks across southwest Canada. The increased southwest flow toward the low draws deeper moisture across the Inland Northwest, ahead of the trailing cold front. That cold front and a supporting mid-level shortwave pass Wednesday afternoon into Wednesday night, with the region also coming under the LFQ of the jet. During the front passage there is deep lift: DIV-Q through the 850-500mb layer, a well-defined 1.5 PV surface, coupled with a defined ribbon of 700-500mb omega (between -5 to -10 microbars/second. All this will result in increasing and modest precipitation chances trough Wednesday afternoon, save for the lee of the Cascades and deeper Columbia Basin in the shadowing effects of the west- northwest flow. I raised PoPs to likely by afternoon for much of the region, aside from the aforementioned shadowed location. I also added a chance of thunderstorms for the afternoon and very early evening over the eastern third of WA and north ID. The aforementioned modest lift encounters a bit of CAPE and LI. MUCAPE is by far the most plentiful with the GFS but even the NAM shows a couple hundred joules/kg or so. So some thunder cannot be ruled out. In kind, I also increased winds with deeper mixing and tighten gradients with the passing front. If some thunderstorms are realized we will have to watch for the combination of these general and convective winds for potential strong gusts. By late Wednesday evening the focus for precipitation begins to shift toward the central Panhandle and southeast Washington, then continues to wane and retreat to the mainly the mountains overnight. Then Thursday and again Friday a weak mid-level shortwave slides by the northern counties. This will keep at least a chance for showers going over northeast Washington and the Panhandle mountains. A few showers cannot be ruled out over the Cascades crest and southeast Washington on Thursday as well, in the west-northwest flow. By Friday, however, the flow turns west to west-southwest. Friday night into Saturday the next more organized system comes to the area. The primary low pressure center remains near the central B.C. coast as it occludes. A warm front glides into the region from the west-southwest by Friday evening, while a 120kt+ jet sags through with an occluded front and mid-level shortwave trough overnight into Saturday. This will renew precipitation chances throughout the region. Yet in a continued westerly flow models keep the lee of the Cascades and deeper Columbia Basin relatively dry and focus the highest precipitation amounts from the Blue Mountains and Palouse into the Panhandle. As the jet stream sags south regional 850mb temperatures drop to between -2 and -3 C near the Cascades to somewhere between -1 and +1 C over eastern Washington and north Idaho. This drops snow levels to near valley floors across the northern and mountain zones and between 2-3kft by Saturday morning. The northern and mountains zones recover to that 2-3kft range by Saturday afternoon, but little change is denoted in the remainder of the Inland Northwest. This will mean some threat of snow. Obviously it is rather early to put a number on how much snow, if any, will fall but some light accumulations are possible during the night and early morning hours. In tandem with these falling snow levels, general temperatures are forecast to drop below normal by Saturday. /J. Cote' Saturday night through Monday...A Low will continue to pass through southern BC throughout this period. The precipitation pattern for the area will continue. The Low will bring a colder airmass into the region causing the snow levels to drop. This will allow the valley locations rain showers to transition into snow during the nighttime hours. The GFS and ECMWF models differ on when the Low will move out of the region. But both show a dry period on Monday morning into the afternoon. Gusty winds start the period then decrease as the Low exits the area. Temperatures are expected to be below normal for this period. /JDC && .AVIATION... 12Z TAFs: A stationary but weakening low pressure centered near KCQV will promote scattered rain showers near most TAF sites through 18Z...and then scattered afternoon convective showers will develop mainly over the eastern reaches of the forecast area...most likely impacting the KGEG area TAF sites and KPUW and KLWS. Between 12Z and 18Z today a moist low level air mass and weak upslope winds have generated IFR ceilings in stratus at KGEG and MVFR ceilings at KSFF..KCOE and imminently at KPUW. These ceilings will break up into low VFR or high MVFR cumulus after 18Z. After 02Z skies will clear with VFR conditions expected at all TAF sites. /MJF && .PRELIMINARY POINT TEMPS/POPS... Spokane 48 34 53 39 58 38 / 30 10 0 10 60 30 Coeur d'Alene 48 30 54 36 57 37 / 50 10 0 10 60 60 Pullman 48 33 54 39 59 37 / 60 20 0 10 60 60 Lewiston 53 37 58 42 65 42 / 50 10 0 10 20 50 Colville 51 31 58 37 60 36 / 50 10 10 20 60 20 Sandpoint 46 31 51 35 54 36 / 60 20 0 10 60 60 Kellogg 44 28 50 35 52 36 / 60 20 0 20 70 70 Moses Lake 55 34 61 42 65 39 / 20 0 0 0 20 10 Wenatchee 53 39 59 43 61 41 / 20 0 0 0 20 10 Omak 54 34 60 39 62 37 / 40 0 0 10 20 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SPOKANE WA 559 AM PDT MON APR 8 2013 IDZ001>004-026-027-WAZ031>038-041>044-091300- NORTHERN PANHANDLE-COEUR D'ALENE AREA-IDAHO PALOUSE- CENTRAL PANHANDLE MOUNTAINS-LEWISTON AREA- LEWIS AND SOUTHERN NEZ PERCE COUNTIES-NORTHEAST BLUE MOUNTAINS- LOWER GARFIELD AND ASOTIN COUNTIES-WASHINGTON PALOUSE- MOSES LAKE AREA-UPPER COLUMBIA BASIN-SPOKANE AREA- NORTHEAST MOUNTAINS-OKANOGAN HIGHLANDS-WENATCHEE AREA- EAST SLOPES NORTHERN CASCADES-OKANOGAN VALLEY-WATERVILLE PLATEAU- 559 AM PDT MON APR 8 2013 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH IDAHO... NORTH CENTRAL IDAHO...CENTRAL WASHINGTON...EAST CENTRAL WASHINGTON...NORTH CENTRAL WASHINGTON...NORTHEAST WASHINGTON AND SOUTHEAST WASHINGTON. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.
The national radar mosaic for the moment the first event began.
1 heavy snow. Local standard time, as filed.
Three to six inches of snow fell at elevations mainly of 3500 feet and higher. Travel across Sherman Pass was hazardous at times due to the snow accumulations on the roadway. This met local late season snow criteria.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2013Every state in 2013This day in weather historyWarnings in Washington, April 2013
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 439746.