232
FXUS66 KOTX 302217
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
317 PM PDT Tue Apr 30 2024

.SYNOPSIS...
Unsettled and cool weather will continue through the end of the
week, with a subtle warming trend Thursday into Friday. The
weekend forecast isn`t certain at this point but its trending
toward another surge of very cool and wet weather, especially on
Sunday. Cool weather with scattered showers are expected to
continue into early next week.

&&

.DISCUSSION...
Today and tomorrow: Widespread shower activity is ongoing under
the influence of a mid level low and cold pool. There have been
quite a few reports of graupel under these showers. They have been
slow moving under the influence of weak vertical shear. Low level
instability and surface relative vorticity look too weak for any
embedded rotation in these showers. Thunder chances have ramped up
a bit on the HREF compared to the older run in eastern WA, ID
Panhandle, and the Blue Mountains (10-30% chance of an isolated
strike). Temperatures are chilly today with highs peaking in the
upper 40s to upper 50s.

The upper low migrates into northwestern MT overnight and brings
in drier northerly flow aloft, especially central WA. Extreme
eastern WA and the ID Panhandle will still be under the influence
of the trough tomorrow so theres additional shower chances.
Temperatures aloft are warmer so I wouldn`t expect much in terms
of thunder chances. This is reflected by the HREF probability of
thunder only showing up with a 10% contour in Clearwater County
tomorrow afternoon. Temperatures tomorrow will be a few degrees
warmer in the 50s to 60s. /Butler

Thursday and Friday...The deep and highly unstable upper level
lows that region has been subject to the last couple of days will
likely move east of the area. On Thursday the core of the low is
expected to head into eastern MT with another moving well of the
coast. A shortwave ridge is expected to build between these lows.
By Thursday evening the ridge axis will likely move onto the WA
coast and over eastern WA on Friday. Mid-level lapse rates on
Thursday will still be sufficient for the production of diurnal
convection, especially over extreme eastern WA and north Idaho.
However given the lack of synoptic scale forcing, much of the
lifting will need to come from orographic ascent which suggests
the coverage will be considerably more limited than what we are
seeing today. Suspect over central WA the chances of precipitation
will be near 0. With the ridge moving atop the Inland NW on
Friday the precipitation chances will be minimal over most
locations, however we cant rule out a small chance of showers
over the ID Panhandle mountains. As for temperatures, 850 mb
readings will range from 4-7C on Thursday climbing to 7-9C on
Friday. This translates to highs generally in the 60s with a
chance of 70 degree or warmer weather over the LC Valley and lower
Columbia Basin.

Saturday and Sunday...this is where the model confidence begins to
tumble considerably. The aforementioned upper level low off the
coast is expected to head inland during this period. Where the low
goes is quite variable. The bulk of the GEFS ensemble members
take the low well to our south, whereas the bulk of the Canadian
and EC solutions bring it much farther north. The GEFS would
likely deliver warm and dry weather if it comes to fruition while
the other solutions suggest significantly cooler and unsettled
weather. On Saturday the range in temperatures over Spokane shows
highs generally in the 60s from the GEFS solutions with highs
struggling to get out of the 50s from the majority of Canadian and
Euro solutions. As cool as unsettled Saturday could be, Sunday is
looking worse. The ENS 500 mb forecast has a 546 low over NE
Oregon with the Canadian showing a similar solution. Meanwhile the
GEFS mean has the low over northern NV, a huge difference. In
these situations it can pay to look at the cluster breakdown
rather than the ensemble means from each model. If anything this
lends even more credence to the cooler/wetter solutions as only
about 25% of the ENS and Canadian member show anything near this
with most of the GEFS solutions supporting warm/dry. The latest
NBM temperatures are catching onto this trend and have already
dropped Spokane`s high temperatures around 8F from the previous
run which is a very significant change this far out in the
forecast. So how cool could it be on Sunday? The latest Canadian
operational model has an 850 mb temperature of -2C and a high
temperature of 41F. The Euro model has a high of 46. We have
trended the forecast cooler than the NBM but not likely cool
enough. We also raised the pops a bit for Sunday based on this
cooler/wetter solution but the NBM QPF isnt likely high enough.
So although there are no guarantees for those with outdoor plans
on Sunday, you might want to prepare for a cool and wet day.

Monday and Tuesday...Model consensus improves significantly as the
deep upper low is forecast to drift off to our east however a
broad weak trough is forecast to persist over the region resulting
in cool and unsettled weather. Highs will likely be in the 50s to
lower 60s. fx

&&

.AVIATION...
18Z TAFS: Another round of showers is developing as the
atmosphere destabilize. Isolated thunderstorms may also develop,
but the main threat will be over the higher terrain of SE
Washington (Blue Mountains), and up over NE Washington around
Republic and Colville.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
There is a 20% chance of thunderstorms on Tuesday mainly across
southern Washington into the Lewiston area, and up over the
mountains of NE Washington. Confidence is any of the TAF sites
being impacted is too low to include in the TAF forecast.

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https://www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        34  59  34  62  37  66 /  20  10   0  10  10   0
Coeur d`Alene  33  55  35  60  37  64 /  10  20  10  10  10   0
Pullman        31  54  32  58  35  63 /  20  20  10  20  10   0
Lewiston       37  61  36  66  39  71 /  30  20  10  20  10   0
Colville       29  61  31  64  34  66 /  20  10   0  20  10  10
Sandpoint      34  53  37  59  37  62 /  30  50  20  40  20  20
Kellogg        34  49  36  56  38  62 /  30  60  20  40  20  10
Moses Lake     33  65  34  67  37  69 /  10   0   0  10   0   0
Wenatchee      38  62  39  65  42  66 /  10   0   0  10   0  10
Omak           34  65  38  68  39  70 /  10   0   0  10   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$