Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 281124
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
624 AM CDT Fri Jul 28 2017

.UPDATE...
Issued at 623 AM CDT Fri Jul 28 2017

Short term high res CAM models continued to show isolated convection
this morning - depicting development in south central and north
central ND - farther north than previous iterations of the CAMs.
Noted isolated cells in the north central: eastern Bottineau;
southern Pierce; central Sheridan counties. Thus expanded slight
chance mention farther north. Also kept mention of thunder out for
the first few hours after sunrise since no lightning strikes evident
and latest SPC analysis indicating very low CAPE, low mid-level
lapse rates, and virtually no bulk shear. Otherwise blended current
temps/winds with forecast values.

&&

.SHORT TERM...(Today and tonight)
Issued at 324 AM CDT Fri Jul 28 2017

Convective development, with timing and anticipated areal extent, is
the main concern in the short term period.

Currently, a flattened upper level ridge was established over
central North America, with embedded shortwaves in the weak flow
aloft over Montana/Wyoming/Dakotas moving eastward. At the surface,
high pressure was over the eastern Dakotas and Minnesota, with broad
low pressure in the Lee of the Rockies from Alberta/Saskatchewan
south to Colorado.

CAM high res model runs continue to depict some isolated convection
developing over mainly southwest and south central ND and over
northwest and north central SD early this morning, associated with
the cluster of upper level impulses drifting eastward across this
area. There has been some weak convection with high/mid-based clouds
over central SD into south central ND early this morning.

The models suggest these showers/thunderstorms would then
dissipate this afternoon as the shortwave continue their eastward
track into the eastern Dakotas.

Attention then turns to the west, where the CAMs indicate convective
development over eastern MT/WY and some models bring convection into
the far western Dakotas this afternoon. More upper level shortwave
impulses moving across the Front Range and some reaching the western
Dakotas as per the global models will bring a slight chance of
showers/thunderstorms to southwestern ND this afternoon. MU CAPE
values are decent, reaching 2000 J/kg with models 0-6km bulk shear
values of 20-25 knots. Higher CAPE and shear values are expected
farther south in SD/NE.

Tonight weak upper level impulses continue moving east across the
state, and spotty chances of thunderstorms will be the rule across
western and central ND Friday night, with better CAPE and shear in
SD/NE.

.LONG TERM...(Saturday through Thursday)
Issued at 324 AM CDT Fri Jul 28 2017

An upper level ridge over the Rockies will persist through the long
term, though shortwaves moving through the flow will flatten the
ridge at times. This will keep off and on chances of showers and
thunderstorms across western and central ND through the long term
period.

Early in the long term:

Weak surface low pressure in the lee of the Rockies Saturday and
Saturday night will keep a moist southerly wind flow across the
Dakotas. Global models in agreement regarding a set of upper level
shortwaves in the flattened Rockies ridge moving east across
Manitoba and northern ND Saturday morning, with another cluster of
shortwave impulses moving out of Montana Saturday morning and
crossing western/central ND Saturday and Saturday night, reaching
eastern ND late Saturday night. This will bring a slight chance of
showers/thundershowers to western and northern ND Saturday
afternoon, with better chances of thunderstorms Saturday night
central and eastern ND. Modest CAPE and 0-6km bulk shear over ND,
with higher instability and shear again over SD/NE.

The upper level ridge builds again on Sunday with the global models
developing very weak upper level impulses over the state. Consensus
of model blends yields a slight chance mention of thunderstorms
Sunday evening southwest through north central.

On Monday/Tuesday there is better consensus in the global models,
which depict a flattening of the upper level ridge with a shortwave
trough moving southeast across central Canada. This system will have
a trailing surface cold front that is progged to move southeast
across ND on Monday, with the front becoming stationary across
northern SD on Tuesday. This will bring a chance of showers and
thunderstorms to western and central ND Monday afternoon and
evening, and chances across southern ND on Tuesday.

Later in the long term:

The upper ridge builds back up over the Rockies, with a mainly dry
forecast for the last half of next week. Seasonable temperatures
with highs in the 80s to lower 90s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 623 AM CDT Fri Jul 28 2017

A few showers and thunderstorms could form over parts of forecast
area today, but guidance is very uncertain in the potential and/or
location. Therefore, elected to keep any mention of VCTS or VCSH out
of the TAF forecast at this time, except at KBIS from 12z-16z given
current light showers evident on radar loops. Otherwise, VFR
conditions will prevail through the period.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JV
SHORT TERM...JV
LONG TERM...JV
AVIATION...ZH


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