Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Hastings NE
501 am CDT Monday Jul 28 2014
Short term...(today and tonight)
issued at 337 am CDT Monday Jul 28 2014
Biggest challenge will be determining risk of precipitation and
thunder late tonight.
A highly amplified Rex block has its axis over The Rockies as a deep
trough is anchored over the eastern United States. We will continue
to lie underneath northwest flow. A surface high is helping to keep
dew points noticeably lower. Judging on recent numerical model
performance...I went closer to the European model (ecmwf) hi res bias corrected for
highs today and nam12bc. Another dry day is in store...but tonight
could be a bit different. Most numerical models are placing at least
some precipitation over our County Warning Area after midnight due to some middle-level
isentropic lift. Precipitation is more likely in our southwest...but
even our northeast could get in on some sprinkles. Thunder is
unlikely...but there could be just enough instability to get some
thunder in our southwestern County Warning Area. High temperatures are a bit lower
than the previous forecast. With the additional sky cover...I did
raise lows a tad compared to the previous forecast.
Long term...(tuesday through sunday)
issued at 337 am CDT Monday Jul 28 2014
Aloft: over the past 30 days the mean pattern has been a western USA
ridge/eastern USA trough. The multi-day mean 500 mb heights from the ec/
Gem/GFS ensemble means agree this pattern will be maintained through
next sun. The last 3 GFS/ec/Gem/UKMET runs are on board as well. So
northwest flow will continue with very little or no dynamic forcing.
Effects on temperatures/precip: this week will be cooler than normal with
below to much below normal rainfall.
Several weak/subtle perturbations /some convectively generated/ will
orbit the subtropical high over the desert SW this week. This
combined with heating of the elevated terrain to the west...
convergence along the front and upslope flow will result in daily
thunderstorm activity west-SW of the forecast area with several cycles of mesoscale convective system
activity. Model quantitative precipitation forecast clustering continues to suggest this mesoscale convective system activity
will track primarily from Colorado southeast into western/southern Kansas and OK.
Surface: the primary polar front will far S of its usual Summer
position this week...quasi-stationary from the Gulf Coast states
back to Texas and then banked up against the Front Range of The
Rockies. High pressure will remain parked over the northern plains.
The daily details...
Tue: tough to get a good read but it's looking M/cloudy. Scattered
showers/sprinkles? May be on-going at dawn as remnants from overnight
activity linger. GFS/ec/NAM/Gem all forecast frontogenesis in the 850-
700 mb layer to weaken and middle-level subsidence to settle in. This
should choke off the shower activity. I may have overplayed the
thunder in a very marginal situation. Soundings suggest some of this
activity may not be tall enough for much ice in-cloud. Confidence is
below average on highs temperatures due to variable cloud cover.
Wed: temperatures probably coolest over north-central Kansas. Another M/cloudy day.
Thunderstorm clusters will be on-going forenoon just SW of the forecast area.
Most of the region will see substantial cirrus cloud cover...
especially in the morning. There is an outside chance the northern fringe
of some of this activity could graze north-central Kansas or extreme S-central
Nebraska. Confidence is below average on highs temperatures due to uncertainty
on cloud cover.
At 50-50 blend of the 15z/21z sref probability of precipitation gave ME 40-50% north and west of
the Tri-Cities in the afternoon. The NAM and sref are on their own
with this potential. Of the global models...only yesterday's 12z/Gem
suggests possible thunder. After coordination with lbf/oax...these
probability of precipitation were removed.
Thursday-Sun: currently looking dry and very comfortable with thunderstorm
activity remaining far to the west and S.
Once we get beyond 10 days /Aug 5/ the ec/GFS/cfsv2 ensemble means
suggest a possible pattern change with a trough forecast to develop in the
west. This will increase the odds in getting beneficial rains. We will
continue to monitor this potential.
July: closing out this month with a cool spell guarantees this July
will go down as cooler than normal. We saw a substantial turn-around
from the very wet June. Only a couple narrow swaths were fortunate
enough to get normal rainfall. Much of the forecast area was drier than
normal...barely receiving 50% of normal.
Aviation...(for the 09z tafs through 09z early Tuesday morning)
issued at 439 am CDT Monday Jul 28 2014
VFR conditions are expected as high pressure continues to
dominate. Some isentropic lift could cause some increase of middle-
level cloudiness toward the overnight tonight. Middle-levels could
actually become broken for a time. There is an outside chance of
some sprinkles...but not enough to introduce a new from group.