Area forecast discussion
National Weather Service Spokane Washington
440 PM PDT Tue Jun 18 2013
Synopsis...
scattered showers and a few thunderstorms will continue Tuesday
night. By Wednesday a wet and cool weather pattern will take hold
of the region. Showery and cool conditions will continue through
the week, with a drying and warming trend expected this weekend.
Wetter and cooler weather will return early next week.
&&
Discussion...
Tonight and tomorrow...offshore low pressure pushing up against
higher pressure inland has a moist and unstable flow in between.
This is being utilized by smaller mesoscale disturbances and other
triggers to generate both surface and forced elevated showers and
thunderstorms through this interval. Hrrr model runs have been
utilized for the short term hours of tonight to time The Breaks in
precipitation and allow for the weakening but not really
dissipating north to south oriented band of showers affecting
locations in The Lowlands from near Moses Lake and up north to
Republic. Tonight a disturbances rotating around the periphery of
the incoming large scale low will fire off more showers and
thunderstorms and take them in a south to north trajectory with
storm motion near 30 mph or so through eastern Washington and
north Idaho overnight and into tomorrow. Number of GFS runs hint
at some of the later convection being highly organized and thus
of longer duration late tonight and into tomorrow which means
there should be a significant amount of rainfall. Thus the
forecast hints at some locations in the north Idaho Panhandle
receiving up to one and one half inches of rainfall in 24
hours...which should increase flow in area rivers and streams. In
addition to the significant rainfall and as is usually the case
gusty wind and small hail is possible near any of these
thunderstorms. /Pelatti
..persistent band of moderate rain Wednesday into Thursday for
the Idaho Panhandle may cause localized flooding...
Wednesday through friday: the biggest concern for the Wednesday
through Thursday time frame will be the amount of rain that will
fall over the inland northwest. A slow moving upper level low will
pivot through northeast Oregon into the Idaho Panhandle and stall
on Thursday into Friday. Deformation band precip (rain wrapping
around the low) should bring a prolonged period of moderate rain
to the Idaho Panhandle, western Montana and southern British
Columbia. We preferred the 00z/12z European model (ecmwf) blended the 15z sref to
build our multi-day precipitation totals. The operational runs of
the NAM and GFS aren't terribly different with their placement of
the upper low and other mass fields, but these operational models
do become noisy from time to time with convective feedback. The
ensemble sref and coarser ec suffer from less feedback which will
hopefully lead to a better basin average precipitation forecast.
The highest precipitation totals from early Wednesday morning
through Friday will likely occur over the Idaho Panhandle, namely
Bonner, boundary and Shoshone counties where as much as 2 to 2.5
inches of rain will be possible through Friday. Areas in far
northeast Washington around Metaline Falls, Newport, and Northport
could get up to 2 inches as well. Rainfall rates don't appear to
be particularly heavy, but the European model (ecmwf) and sref (which will be
conservative) suggest the heaviest rates will occur Wednesday
morning with as much as a half to three quarters of an inch in 6
hours within a localized band. Most areas should be able to handle
these precipitation rates. The 12z-18z NAM has almost double these
rain rates (up to 1.25 inches per 6 hours) which could cause some
problems on creeks and small streams.
Concern area #1: the Idaho Panhandle and southeast British
Columbia. A Flood Watch may be necessary for Wednesday for
portions of the Idaho Panhandle for creeks and small streams.
Another concern will be the large amount of precipitation from
Wednesday through Friday over the Kootenai basin in southeast BC,
northwest Montana and far north Idaho. Rises are forecast on the Kootenai
at Bonners Ferry. The potential for more rain next week is not
particularly good news, but it is early to say whether rains next
week will be significant enough to generate run-off.
Concern area #2: the burn scars in central Washington around
Wenatchee, Chelan and Entiat. Fortunately, the deformation band
with the upper low will be well east of the burn scar area on
Wednesday. There is a small chance on Thursday, that this band
will pivot into central Washington, but it will not likely
maintain precipitation intensity into Thursday. There will also
be a small chance of thunderstorms on Wednesday. The atmosphere
does not appear to be particularly unstable with a 500mb temp of
only -18c to -19c. There should also be a good deal of low
cloudiness Wednesday which should inhibit surface heating
throughout the day. All-in-all, the threat of flash flood appears
to be low over the burn scars through Friday. /Gkoch
Friday night thru Sunday night... lingering showers and cool
temperatures will continue over eastern sections of the County Warning Area Friday
night as the persistent upper low slowly moves east from the
southern part of the Idaho Panhandle. Differences in timing
between the ec and GFS cast doubt on how fast the system will move
east on Saturday and while the Cascades and basin will have mostly
clear skies and warming temperatures, showers may linger over the
Idaho Panhandle. By Saturday night and early Sunday all models
agree that the County Warning Area will be in between systems and under a weak
short wave ridge. The ec then brings in the next system off the
Pacific by Sunday afternoon with an increasing threat for showers
over the Cascades. Precip is on the increase Sunday night as the
ridge moves quickly east and the flows becomes westerly. Jl
Monday and Tuesday...it looks like another moist storm system will
be affecting the inland northwest next week, bringing increased
rain chances to many areas. There is decent model agreement
regarding this system, with only some slight timing differences.
We went ahead and bumped up precipitation chances, especially
along the Cascade crest. With what is going to fall over the next
couple of days, anything of significance rainfall wise may cause
some hydrology issues. This is definitely something to watch out
for. TY
&&
Aviation...
00z tafs: another round of showers and thunderstorms will affect all
of the taf sites this evening with moderate rain and some MVFR
cigs. A band of moderate to heavy rain will develop late tonight
along the Washington/Idaho border, and persist through much of Wednesday. This
will bring IFR conditions to most of the eastern taf sites all day.
Kgeg will be on the western edge of this band and conditions may
improve a bit in the late afternoon. Ksff and certainly kcoe will
feel the brunt of this event. To the south, kpuw and lws may see
some improvement in the afternoon but I didn't have enough
confidence in this. Kmwh and keat should remain out of the action
for the most part and will actually have better conditions tomorrow
than today. Rj
&&
Preliminary point temps/pops...
Spokane 52 54 45 55 44 61 / 80 100 80 80 50 60
Coeur D'Alene 52 54 46 54 42 60 / 90 100 100 90 50 60
Pullman 49 53 44 56 42 60 / 80 100 70 60 30 60
Lewiston 54 58 49 64 44 67 / 70 100 70 60 20 50
Colville 51 63 50 57 48 67 / 90 100 100 100 60 50
Sandpoint 50 56 46 53 45 60 / 100 100 100 100 60 60
Kellogg 50 51 44 51 39 57 / 100 100 100 100 50 60
Moses Lake 55 66 51 65 49 69 / 70 50 50 60 30 30
Wenatchee 56 66 52 64 51 68 / 40 40 50 60 40 30
Omak 53 66 51 64 50 69 / 60 80 70 80 60 50
&&
Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&
$$
