Area forecast discussion
National Weather Service Spokane Washington
1056 PM PDT Mon Jun 17 2013
Synopsis...
an increasing chance of showers and thunderstorms comes to the
inland northwest today through Tuesday. By Wednesday downright wet
and cool weather envelopes the region. Showery, cool conditions
will continue through the week, with a drying and warming trend by
the weekend.
&&
Discussion...
quick evening update to mention gusty winds and heavy rainfall in
and near thunderstorms overnight. Elevated convection fired up as
expected with small hail and occasional lightning fairly
widespread the last 5 hours. Activity will eventually diminish
overnight and allow the atmosphere to regroup for the next round
Tuesday evening. The 0z models have some disagreement in where the
main threat will be with the NAM being the outlier placing all
convection in Montana. The GFS is in agreement with the old ec
keeping scattered showers and thunderstorms over Washington and
the best potential for significant activity over the Idaho
Panhandle. Overnight crew will have a challenging forecast to
determine specifics of Tuesday evenings convection...at this time
content to leave forecast as is advertising scattered evening
convection mainly east of todays showers.
&&
Aviation...
06z tafs: several amendments this evening to keep up with passing
thunderstorm threats. Winds have been erratic in many locations as
expected but generally expect winds to increase out of the west
southwest overnight and then diminish later Tuesday. Another round
of convection likely late Tuesday afternoon and evening with the
focus slightly shifting east of todays showers.
/Ab
&&
Previous discussion... /issued 506 PM PDT Mon Jun 17 2013/
Synopsis...
an increasing chance of showers and thunderstorms comes to the
inland northwest today through Tuesday. By Wednesday downright wet
and cool weather envelopes the region. Showery, cool conditions
will continue through the week, with a drying and warming trend by
the weekend.
Discussion...
tonight and tomorrow...large area of low pressure off the coast
and slowly moving toward the inland with time against higher
pressure further inland. This synoptic positioning will allow for
a somewhat warm and unstable southerly flow primarily from the
south with various shortwave triggers rotating around the
periphery of the offshore low coming up through it and passing
through eastern Washington and northern Idaho in a mostly south to
north trajectory. This warm trajectory negates any shadowing off
the Cascades and in fact pops remaining highest at times over the east
slopes of the Cascades and the vicinity lowlands because of this
setup. The small mesoscale shortwaves triggers passing through
tonight along with the instability mentioned allow for a prolonged
mention of thunderstorms of the elevated nature moving quite
quickly with estimated storm motion to the north near 30 mph or
so. At the same time the air-mass overhead supports production of
surface based showers and thunderstorms as well but those will not
move as quickly...they should still move north...but not as
fast...more like 5 to 10 mph or so. Due to this above reasoning
the forecast for tonight and tomorrow remains cluttered with
various mentions of showers and thunderstorms and associated
moderate cloud cover. As is typically the case wind will be gusty
and erratic near any thunderstorm. /Pelatti
.Very wet with below average temperatures Wednesday and Thursday...
Tuesday night through thursday: upper level closed low that has
been sitting off the Pacific northwest coast for several days will
finally move inland and produce a very wet and cool period.
Tuesday night the low will move inland and by Wednesday it will be
across northern Oregon...with Thursday it moving up into northern
Idaho. As the low slowly moves across the pac northwest it will produce
periods of rain starting Tuesday evening and continuing through
Thursday. The best forcing for heavier rain amounts will be mainly north
and east of Spokane...across northeast Washington and the northern Idaho
Panhandle. The valleys could see 1.00-1.50 inches of rain with the
higher terrain possibly seeing two inches of rain. There will be
some isolated pockets up in extreme north Idaho and Washington...mainly
from Northport east towards Porthill that could see 2.50 inches of
rain. The northern Cascades will also be another location to see
up to an inch of rain or snow as snow levels will lower as the low
moves in. Snow levels will generally be 6000 feet or higher
through the event. The area which should receive the least amount
of rain will be south and west of Moses Lake where they will see a
quarter of an inch or less. The heaviest rain will fall Wednesday
into Wednesday night.
Thunderstorm potential will remain high Tuesday evening as the
first strong wave pushes into the area providing a good kicker for
thunderstorms to fire off. Generally the threat will be
everywhere, but models are showing the best instability across
north Idaho. By Wednesday thunderstorms remain a concern, mainly
north and east of the low, so over eastern Washington and north Idaho. And by
Thursday the our chances lessen even more with the best potential
being across north Idaho. Heavier amounts of rain are possible under
any thunderstorm that develops with this system as it moves
through, and the precipitation amounts mentioned in the previous
paragraph does not include extra rain amounts from thunderstorms.
Temperatures Tuesday night will be around average for this time of
the year. However by Wednesday, with all the rain and cloud cover
we are expecting, do not anticipate temperatures rising that much
through the day. Temps Wed will be 15-20 degrees below average for
this time of the year. Temperatures will remain below average for
Wed night and thur. /Nisbet
Friday and Saturday...the upper level low pressure that will be giving
US our chilly temperatures and increased rain chances should begin
exiting the inland northwest this weekend. This will bring a
drying trend from west to east.
Friday should be the last day of higher rain chances, as the
upper low moves to near the northeast Washington/Idaho Panhandle
border. The low should begin to accelerate off to the east through
Saturday, taking most of the lift and dynamics with it. However,
ample low-level moisture will remain after the week's rainfall.
Therefore, we did not remove precipitation chances altogether. Low
chances will remain, especially over the elevated regions of
northeast Washington into the Idaho Panhandle. TY
Sunday and monday: the shortwave ridge expected this weekend will
be transient. By Sunday night, the GFS, GFS ensemble mean, and the
European model (ecmwf) are in good agreement that the 500mb ridge axis will migrate
into western Montana. Sunday should remain dry. By Monday, we
should experience increasing mid-upper level southwest flow
bringing the increased threat for showers and thunderstorms.
/Gkoch
Aviation...
00z tafs: minor updates to the 00z taf package with overnight
convection still looking like a good bet. Some model disagreement
in the initiation of the elevated convection...leaned toward the
NAM solution which is consistent with previous runs and places
most activity just east of the Cascades late this evening.
Showers diminish during the early morning hours with the last 6
hours of the taf highlighted by surface based convection again
firing up near keat and sct to bkn skies elsewhere. Winds
generally southwesterly and locally gusty./Ab
&&
Preliminary point temps/pops...
Spokane 56 75 52 55 46 59 / 50 50 80 100 80 70
Coeur D'Alene 55 75 53 56 47 60 / 50 50 90 100 100 90
Pullman 50 72 50 56 43 59 / 20 50 80 100 70 50
Lewiston 57 82 55 62 49 66 / 20 40 70 100 70 50
Colville 53 79 51 62 48 61 / 50 60 90 100 100 80
Sandpoint 52 81 50 57 46 59 / 50 50 100 100 100 90
Kellogg 55 77 50 53 43 54 / 20 40 100 100 100 80
Moses Lake 57 75 55 63 50 69 / 50 50 50 60 40 30
Wenatchee 60 74 57 63 52 64 / 40 60 40 60 50 50
Omak 54 77 53 60 49 65 / 40 70 60 90 70 60
&&
Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&
$$
