Area forecast discussion
National Weather Service Bismarck ND
655 am CDT Monday may 20 2013
Update...
issued at 655 am CDT Monday may 20 2013
No signficant changes to previous forecast...or Wind
Advisory/Flood Watch headlines. Showers continue to increase in
coverage and intensity across the northeast half of the forecast
area and will continue to spread westward through the morning hours.
&&
Short term...(today and tonight)
issued at 420 am CDT Monday may 20 2013
Forecast highlights/concerns in the short term period will
continue to focus on the storm system over the region...bringing
additional rainfall amounts through tonight and potential flooding
to west and central North Dakota.
Currently...large upper level low over the northern plains is
centered over central South Dakota...with multiple embedded
vorticity maximums/cyclonic circulations rotating around/within
the large low. Moderate to heavy rain right now is focused
underneath the systems trowal...stretching from just north of the
international border back southwest across eastern Montana.
Scattered showers for the most part elsewhere in the County Warning Area.
Precipitation growing in aerial coverage across eastern North
Dakota moving back west as embedded energy pivots back west
around the low. Decent aerial coverage of rain currently over the
James River Valley which earlier had a few embedded thunderstorms
with MUCAPE 250-500 j/kg just to the north of a stationary
boundary. Surface low pressure over eastern South Dakota
maintaining a tight pressure gradient across my west and north.
Winds continue to gust to around 40 miles per hour across the Wind Advisory
area...sometimes higher to near 45 miles per hour.
The center of the upper low is forecast to lift into southeastern
North Dakota today as does the associated surface low...then
retrogrades back southwest to over central South Dakota by early
Tuesday morning. Embedded energy rotating within the low and
across North Dakota will maintain moderate to at times heavy
rainfall to much of the state through the short term period...so
will maintain categorical probability of precipitation and continue to mention possible
heavy rain. See hydrology discussion below concerning this and the
Flood Watch.
Tight pressure gradient is maintained west and north...and
eventually develops across the south central late today/this
evening. Opted to keep the Wind Advisory confined to my west and
north central for now...but may need to be expanded into the south
central if we can mix stronger winds to the surface after 00z.
One thing of interest via the 00z GFS/ec...and the 00z/06z
NAM...is the cooling aloft near 850mb to freezing late
tonight/early Tuesday west and central. However...the GFS
maintains a warm layer between 700-850mb...as well as a warm layer
from 850mb to the surface. The 06z NAM is not as warm...and is
subfreezing over my southwest from 850mb and up...and also
advertises a cooler boundary layer. Will keep the precipitation
type as all rain...but would not fall out of my chair if a flake
or two actually reached the ground across the higher terrain of
the southwest where lows tonight are forecast in the upper 30s.
Long term...(tuesday through sunday)
issued at 430 am CDT Monday may 20 2013
The main forecast issue through the long term period will be ongoing
river and overland flooding concerns. See hydrology discussion below
for details. On Tuesday...there is decent model agreement regarding
the path of the closed upper low to the southeast of the forecast
area...and associated showers. Additional quarter to half inch
amounts are possible through Tuesday night...especially in the James
River Valley. Expect cool and breezy conditions...with highs in the
50s most locations. Light rain will diminish south Wednesday
followed by gradually warming temperatures into the weekend as upper
ridging returns to the northern plains. Southwest flow will bring
increasing moisture into the state...and there will be chances for
showers and storms every day from Friday through the weekend.
&&
Aviation...(for the 06z tafs through 06z Monday night)
Issued at 420 am CDT Monday may 20 2013
Moderate to heavy rainfall will continue/redevelop over all
terminals through the taf period with MVFR/IFR cigs/vsbys.
&&
Hydrology...
Issued at 420 am CDT Monday may 20 2013
A Flood Watch remains in effect for all of western and central
North Dakota through Monday night. Multiple river points are
forecast to reach action stage or exceed flood stage thanks to the
rainfall the past few days...and the expected rainfall through
Tuesday. All the forecasts are very highly dependent on how much
rain falls over the next 36 hours so users are asked to check back
frequently for updates. Will also have to monitor for overland
flooding and local rises on some of the smaller creeks and
streams.
&&
Bis watches/warnings/advisories...
Flood Watch through Tuesday morning for ndz001>005-009>013-
017>023-025-031>037-040>048-050-051.
Wind Advisory until 1 am CDT /midnight MDT/ Tuesday for
ndz001>005-009>013-017>019-021-031>033-040-041-043-044.
&&
$$
Update/long term...rp Kinney
short term/aviation/hydrology...New Hampshire
