Area forecast discussion
National Weather Service Grand Forks ND
1148 PM CDT Tuesday may 21 2013
Update...
issued at 1148 PM CDT Tuesday may 21 2013
No updates needed...
The forecast remains on track with clearing sky slowly sagging
southward...now along the international border. Expect scattered
showers ahead of this clearing line.
See the hydrology section for the latest information on the
Renwick dam situation.
&&
Short term...(this evening through Wednesday night)
issued at 329 PM CDT Tuesday may 21 2013
The focus today was on the serious flooding situation in
northeastern ND. Good news is that the very last of the light
showers are moving through and from 00z Wednesday to 12z Friday dry weather is
forecast for that Grafton-Walhalla-Cavalier areas.
Upper low near Sioux Falls will continue to drop south and then east
the next 24 hours allowing for slow clearing now in southern
Manitoba (portage-winnipeg) to drop into far northern ND by 12z Wednesday and
then southward reaching the far southern forecast area Wednesday evening. Will
keep in chance probability of precipitation for precipitation tonight in the central-southern forecast
area and only in the far south-southeast Wednesday morning-midday.
High pressure and clear-partly cloudy sky for Wednesday night. A bit
cooler than average. Could be some fog Wednesday night with light winds
and clear sky due to all the water in the fields and ditches.
Long term...(thursday through tuesday)
issued at 329 PM CDT Tuesday may 21 2013
Nice day on Thursday with light winds and sunshine then clouds to
increase late Thursday night into Friday from the west as the next
short wave moves into the High Plains. Will maintain some low probability of precipitation
for Friday in eastern ND and the valley for some warm advection light rain
showers.
12 UTC GFS/European model (ecmwf) are in good overall agreement Friday night through
early next week. Both show a ridge aloft aligned across the eastern
Dakotas through Sunday...then breaking down somewhat early next week
as energy from a Pacific northwest trough moves along the Canadian
border. Meanwhile...a northwest to southeast oriented middle-level
thermal boundary stalls across the northern plains...providing a
focusing mechanism for showers and thunderstorms. Best chance for
measurable rain appears to be Friday night and then again Sunday
night through Tuesday as a couple short-waves rotate across the High
Plains and provide additional lift for convective development. All
blend guidance handles this well and will keep chance probability of precipitation through
most of the long term forecast. With advancing warm front...will see
a gradual warming trend through the period from the middle 60s on
Saturday to the middle 70s by next Tuesday.
&&
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1148 PM CDT Tuesday may 21 2013
MVFR ceilings will continue to slowly move to the south...with VFR
ceilings moving into the region from the north...and eventually
clearing on Wednesday. Expect gusty east/northeast winds Wednesday
afternoon.
&&
Hydrology...
issued at 650 PM CDT Tuesday may 21 2013
Rain showers will be on the wane from this evening through Wednesday
allowing river forecasting to be more runoff as opposed to quantitative precipitation forecast
based. River flood warnings remain in effect at Walhalla and Neche
along the Pembina river with Walhalla having crested earlier.
Biggest forecast change is along Park River at Grafton where the
copious rainfall has triggered rapid stage rises toward major and
ultimately near record flood levels.
River flood warnings are now in effect for most of the mainstem red
as well as the southern valley Minnesota tributaries to the red.
These points are all expected to achieve minor flood stage save for
Oslo where moderate flooding is forecast.
Areal flood warnings will be in effect for Pembina...eastern
Cavalier...and Walsh counties through Thursday. By then areal
flooding should become less of a concern with a dearth of
precipitation and the chance for some drying with warmer
temperatures.
The Flash Flood Watch remains in effect for parts of Pembina County
as heavy rainfall over the past few days has caused flood waters to
approach the top of the spillway at the Renwick dam. Water
remains very high and is being held back by a constructed earthen
levee on top of the dam structure. Officials continue to monitor
the dam and the new Clay levee for any erosion. There are several
old retention dams to the west of the Renwick dam...and with the
large amount of water in the area these dams could fail. If one of
these older dams to the west did fail...the temporary levee on top
of the Renwick dam would no longer be able to hold back
water...and flooding would be imminent for the cities of
Akra...Cavalier...and Bathgate. The Pembina County emergency
management anticipates a possible breach within the next 12
hours...and have ordered a mandatory evacuation for the area
immediately downstream of the Renwick dam...including the city of
Cavalier.
&&
Fgf watches/warnings/advisories...
ND...Flash Flood Watch through Wednesday afternoon for ndz008.
Minnesota...none.
&&
$$
Update...tg
short term...Riddle
long term...Riddle/Rogers
aviation...tg
hydrology...wjb/tg/jh
