Area forecast discussion
National Weather Service Grand Forks ND
1006 PM CDT Sat may 18 2013
Update...
issued at 1006 PM CDT Sat may 18 2013
Thunderstorm complex approaching from the west is slowing down
(was moving around 20 knots an hour ago...now moving around 10
knots). This is causing very heavy rainfall...but also means that
this complex may not quite make it into the forecast area. Southerly low
level flow is increasing as the mean upper trough shifts
east...and this is likely halting the eastward progress of this
complex. 01z hrrr stalls this complex and actually dissipates the
activity. The main focus overnight appears that it will come from
the south along with intense moisture advection. Slightly adjusted
probability of precipitation to account for the above thinking. The severe threat still
appears limited for this forecast area. The storms just west of the forecast area are
severe...but the slowing movement will likely weaken these storms.
The low level jet for later tonight is only around 25-30
knots...and any severe threat given the weaker instability should
be limited.
The main concern is likely flash flood/heavy rain given the slow
storm movement along with precipitable waters approaching 1.5 inches. Will
mention localized heavy rain in the grids...but a Flash Flood
Watch is not needed if the activity from the West Falls apart
before the southern activity moves into the region.
&&
Short term...(this evening through Sunday night)
issued at 300 PM CDT Sat may 18 2013
All eyes on any convective development late this afternoon-evening in southeast
ND-west-central Minnesota. Surface map shows a broad surface low in the Mobridge South Dakota
area with a boundary (could be called a warm front) from Mobridge
to Oakes then to Valley City then to Hillsboro then east to north
of dtl-pkd-brd then into far northwest Wisconsin. In far southeast ND and
adjacent parts of west-central clouds cleared out enough today for surface
heating and temperatures in the 77 to 81 degree range. Satellite shows
what appears to be a cumulus cloud boundary from Hillsboro to
along Clay-Norman Colorado line to north of Park Rapids. South winds
south of this feature near 10-13 kts while north winds 5-8 kts
north of this feature. Storm Prediction Center shows little cin and 1500 j/kg cape and
sufficient bulk shear. But upper levels dont show any big thing to
set stuff off. 17-18z hrrr reflectivity does show one cell trying
to get going in Norman Colorado. Minnesota 22-23z period but then it dissipates
this evening.
Much of northeast South Dakota has seen high clouds today and dew points in the
50s and Storm Prediction Center does have some surface based cin in this region. Thus may
be hard to get anything going there. But hrrr wants to generate
some activity axn-stc area by 03z.
Also some storms near Black Hills in western South Dakota. Some WRF models
indicate this area organizing much like last evening and moving
east-northeast into southeast ND-west-central Minnesota overnight. So various
scenerios to play out.
Overall would expect organization of some activity this evening in
ND/SD/MN border regions and then spread north and east tonight so
will stick with high probability of precipitation tonight though confidence at any one
hour is low. Also quantitative precipitation forecast amount is not certain. Plus only area that
much more than 1 inch of rain last night was eastern Otter Tail
County with 0.50 to 1 inch northern Wilkin-southeast Clay into Wadena
counties. This area could take the rain. Otherwise...rain amounts
in the valley were mostly 0.50 or less with a few exceptions. With
uncertainity in how things will play out tonight did not feel
confident in issuing any flash flood watches for our forecast area.
Models actually bring in higher precipitable water (1.6) into area Sun afternoon-nigh in
general rainfall around the upper low in South Dakota and this is in when
most widespread heavier rainfall may occur. Thus if true...gives
US time to see what falls this evening before issuing any headlines.
Kept high probability of precipitation Sunday into Sun night most all areas.
Long term...(monday through saturday)
issued at 300 PM CDT Sat may 18 2013
Upper low and surface low will be over southern South Dakota Monday into Tuesday with
moisture wrapping around into ND/northwest Minnesota Monday-Tuesday period with
general rainfall. Kept probability of precipitation high.
For Tuesday night-Friday...models have been most consistent in
beginning to move the stacked northern plains low pressure system eastward
in the middle week period. Tuesday night into Wednesday shows the
tappering off of very light rain with persistent north-easterly
blayer winds. Intruding dry air from western ont should lead to markedly
diminishing cloud Clover Wednesday evening. Increasing high pressure
over western ont and the Lake Superior area on Thursday and Friday should swing
winds from the soouh east and keep an overall drying airmass over
the Red River and most of Minnesota. A warmig ridge aloft and increased
low pressure in eastern Montana does increase the risk for scattered showers
and thunderstorms into eastern ND by late Friday and across the forecast area by
Saturday.
&&
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 716 PM CDT Sat may 18 2013
IFR/LIFR ceilings affecting kbji and kdvl...with MVFR ceilings affecting
ktvf and kgfk...as these site are within low level northerly flow.
Not if these conditions will continue through the night. Most
guidance suggests that an area of thunderstorms and/or showers
will move through these sites...which should briefly raise ceilings.
Until then...expect the lower ceilings to continue. Ceilings should lower
through the day on Sunday with shower chances increasing. For
kfar...expect thunder chances to incrase by midnight...along with
lowering ceilings.
&&
Hydrology...
issued at 300 PM CDT Sat may 18 2013
When ncrfc ran the model today using 24 hour quantitative precipitation forecast it brought several
points above flood stage. These include Fargo/Sabin/Dilworth/Hawley
and Hendrum. Since these rises are based on forecast precipitation went ahead
and issued a River Point Flood Watch for these 5 points. The forecast
quantitative precipitation forecast also brought Wahpeton/East Grand Forks and Oslo back above
action stage so issued river statements on these. Only Drayton and
Pembina remain in a flood statement.
&&
Fgf watches/warnings/advisories...
ND...none.
Minnesota...none.
&&
$$
Update...tg
short term...Riddle
long term...Riddle/gust
aviation...tg
hydrology...godon
