Area forecast discussion
National Weather Service Bismarck ND
916 PM CDT Tuesday Jun 18 2013
Update...
issued at 916 PM CDT Tuesday Jun 18 2013
Latest Bowman Doppler radar shows an area of showers and isolated
thunderstorms beginning to impinge into southwest Harding County in
South Dakota. The 850 mb-h30 mean wind would continue to move the
precipitation area from southwest to northeast this evening. The
the latest rap initially has the areal extent of the aforementioned
precipitation too far north...and will make adjustments with a
heavier blend of the NAM overnight. Still expecting isolated
thunderstorms into far southwest North Dakota as previously
forecast...as a 850 mb-700 mb saturated potential temperature ridge axis resides
in close proximity in far southwest North Dakota and the ongoing
convection...along with 850 mb-500 mb lapse rates of 7c/km. The activity
should weaken thereafter...and have tapered off probability of precipitation to less than
measurable into south central North Dakota overnight. Although
cloud debris/altocumulus castellanus (altocumulus castellanus) should be visible
later tonight into early Wednesday morning as instability shifts
into North Dakota. Elsewhere...clouds are also increasing in
northeast Montana as a cirrus canopy shifts east from the
thunderstorms in north central Montana. Will continue to increase
clouds overnight west and south central. Expectations are isolated
convection will be confined to the southwest zones overnight and
dry conditions elsewhere.
Update issued at 624 PM CDT Tuesday Jun 18 2013
Latest water vapor imagery this evening shows a middle/upper level
disturbance rotating through central North Dakota at this time.
Visible satellite imagery and surface observation show scattered middle level
clouds stretching from Roseglen to near Dickinson...with a scattered
fair weather cumulus field across south central and east central
North Dakota. With a 700 mb-500 mb ridge axis anchored from Williston to
Bismarck and into Sioux Falls South Dakota tonight...expect a dry
night along and east of the aforementioned ridge axis.
Attention this evening and overnight turns to an upstream shortwave
over southeast Wyoming. This is generating thunderstorms in the
higher terrain of Wyoming...with a large middle/high level cloud
canopy expanding over eastern Wyoming and southeast Montana. This
is moving northeast and will slide into our southwest zones this
evening. The latest rap advects some light precipitation into the
far southwest zones toward 06z. The 18z GFS is more robust in
generating a larger swath of light precipitation late tonight
through middle morning Wednesday in southwest North Dakota and just
grazing our south central zones. However other models delay the
showers/thunderstorms with this shortwave until Wednesday
afternoon and evening. Will await the 00z data before making any
changes beyond tonight. Will also monitor the convection
approaching the southwest this evening/overnight. Only updates
this evening was to hourly observation and to increase sky grid trends in
the southwest as mentioned above. The cloud debris may make it
into south central North Dakota before sunrise Wednesday.
&&
Short term...(this evening through wednesday)
issued at 324 PM CDT Tuesday Jun 18 2013
Surface trough and associated warm frontal boundary in eastern
Montana will be the focus for scattered thunderstorms late tonight
and Wednesday afternoon. Anticipate some thunderstorms will fire
over the higher elevation areas in Wyoming/Montana/South Dakota
and drift into southwest North Dakota late tonight. On Wednesday one
limiting factor will be a slowing evolving elevated mixed layer
that may cap thunderstorms over western North Dakota Wednesday
afternoon. However believe the increasing low level jet and
significant cape values justify scattered thunderstorms across
west and central North Dakota Wednesday afternoon. Winds on
Wednesday should approach but remain below Wind Advisory criteria
southwest...probably 20 to 35 miles per hour.
Long term...(wednesday night through tuesday)
issued at 324 PM CDT Tuesday Jun 18 2013
The main forecast issue through the long term period is convective
trends and potential for periods of strong to severe storms...some
accompanied by heavy rainfall.
The runs of the GFS/European model (ecmwf) are in general agreement with a slower
progression of a large closed upper low in the Pacific northwest
early in the period...with the NAM fastest in bringing the main
synoptic features eastward. Have favored the GFS/ec solutions for
probability of precipitation Wednesday night and Thursday. There is some potential for an
mesoscale convective system to clip northwest counties late Wednesday night into Thursday
morning...fueled by a 40-50 knots low level jet. The main
decision-making element was when/where the strong middle-level cap
would inhibit convection...because otherwise plenty of cape and
shearing for severe thunderstorms.
Wednesday evening the axis of the middle-level cap of 10-14c is
situated over Wyoming/eastern Montana and nudging into South Dakota
and far southwestern North Dakota. The cap builds during the evening
northward and eastward across the Dakotas. At this time it appears
the best chance of severe thunderstorms begins in far western North
Dakota late evening Wednesday or early morning Thursday...with
severe thunderstorms possible. The storms move eastward into
central North Dakota between midnight and daybreak Thursday morning.
Thursday the accompanying surface front is prognosticated to be oriented
north-south across central North Dakota...with the best chances of
thunderstorms in northwest and central North Dakota Thursday
morning...and shifting to central North Dakota Thursday afternoon
and into Thursday evening. The best chance for severe weather
Thursday is in the northwest and central.
Friday and Friday night looks to be the time frame for widespread
moderate to heavy rainfall. Continued upper level energy and low
level moisture with a surface low becoming established over the
Central Plains and overrunning precipitation north of the low is
favored for the heaviest rainfall. Widespread rainfall amounts of 1
to 2 inches is possible.
The models continue to depict the upper level low maintaining its
presence over The Rockies with southwest flow over North Dakota with
multiple upper level energy impulses moving across the state in the
upper flow. The models bring the upper low across the state Sunday.
Precipitation chances lessen Monday and Tuesday...but zonal flow
aloft would allow some upper level impulses to support showers and
thundershowers into early next week.
Temperatures are expected to be seasonable through the period...with
highs in the 70s/lower 80s...and lows generally in the 50s and 60s.
&&
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 624 PM CDT Tuesday Jun 18 2013
VFR ceilings and visibilities expected through the taf period. Scattered/broken middle
level clouds will develop at kdik overnight with mainly clear
skies elsewhere. Chances for shower and thunderstorms will
increase mainly after 18z Wednesday into Wednesday night. A thunderstorms in the vicinity
has been added to most aerodromes Wednesday afternoon.
&&
Bis watches/warnings/advisories...
none.
&&
$$
Update...Kansas
short term...warm air advection
long term...jv
aviation...Kansas
