Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Hastings NE
1223 PM CDT Monday Apr 27 2015

Short term...(today and tonight)
issued at 320 am CDT Monday Apr 27 2015

Quiet weather is forecast through the short term periods with
temperatures trending closer to seasonal normals. The Central Plains
will be between weather systems as an upper low pressure system
tracks well to our south across Texas...and to the north a shortwave
trough translates across the Dakotas into the upper Midwest. A dry
airmass will remain in place across our region and this combined
with more sunshine than recent days will lead to fairly seasonal
high temperatures averaging in the upper 60s. Model forecast
soundings indicate mixing to around 800 mb this afternoon which will lead to
a period of steady winds at times. For temperatures tonight have trended
with the cooler guidance in the dry airmass with good radiational
conditions...with lows averaging in the upper 30s to around 40f.

Long term...(tuesday through sunday)
issued at 435 am CDT Monday Apr 27 2015

Overall...not much change to the big-picture expectations of this
6-day period compared to 24 hours at least for now the
primary synoptic scale features of the 00z NAM/GFS/ECMWF are in
pretty darn decent agreement. What this means for the local area
is that there is high confidence in a prolonged return to slightly
above average temperatures with highs mainly in the 70s and lows
mainly in the 40s to near 50...with no frost/freeze opportunities
evident through at least may 3rd and likely beyond. Precipitation-
wise...with the exception of an iffy chance of sprinkles/possibly
brief light showers mainly in the northwest 1/2 of the County Warning Area Tuesday
afternoon...there is high confidence in prevalent dry conditions
especially the Tuesday-Thursday night time frame. Have also left
Friday daytime void of precipitation mention at least for now...but this
is no guarantee to stay this way. Thereafter...although it
probably makes the forecast "sound" wetter than it probably will
end up being...maintained 4 straight periods of primarily slight
chances of showers/thunderstorms from Friday night-Sunday. As is
typical of weakly forced convective rain chances...confidence in
the details of how Friday night-Sunday play out is quite low at
this time. One minor change from previous forecast was to broad-
brush these low precipitation chances to include the entire County Warning
it's virtually impossible at the day 5-7 time range to attempt to
"rule out" one portion of the County Warning Area versus another.

As for weather elements that warrant inclusion in the hazardous
weather outlook (hwogid)...the only thing at this time is the
generic mention of thunderstorms Friday night Onward. It is far
too early to even begin digging into the details of whether or not
these weekend chances carry much risk for strong to severe
storms...and not surprisingly Storm Prediction Center doesn't even make a mention of
the possibility in the latest day 4-8 outlook due to the potential
being too low that far out in time. Furthermore...none of these
storm chances currently appear tied to a larger-scale/organized
low pressure system. All this being said...the time of year
dictates that almost any chance of storms bears watching...and
although very subject to change...the latest instability/shear
forecasts from the European model (ecmwf)/GFS suggest that at least a few strong storms
could be supported. Briefly looking just beyond the current valid
forecast period...there are at least preliminary signs that
potentially/more widespread thunderstorm chances could arrive
during the may 4-6 time frame next week.

With the larger scale scene's time to turn to more
detail in 12-24 hour blocks:

Tuesday daytime: while the vast majority of the County Warning Area should remain
dry the majority of the day...the previous forecast introduced a
slight chance of sprinkles for the afternoon hours to mainly the
northwest 1/2 of the County Warning Area...and this forecaster sees no reason not
to let this minor precipitation chance ride for now. In the middle-upper
levels...models are in good agreement in keeping the eastward-
departing Southern Plains closed low well to our south...while the
trailing southwestern portion of a fairly weak trough extending
southwestward from Canada sags into the local area during the
afternoon...accompanied at the surface by a very weak cold front.
Although convective instability should be almost none with these
features and low-level moisture will be sparse...model soundings
and plan-view forecasts suggest there could be just enough forcing/middle
level saturation to spark a narrow line of sprinkles/possibly
light showers mainly in northwest zones. Should any of this
activity could be more of a virga event than
anything. Apart from this seemingly minor rain chance...the day as
a whole should average mostly sunny-partly cloudy with a
prevailing north-northeast breeze generally 10-15 miles per hour. Made very
little change to high temperatures...aiming most areas into a rather
uniform expectation of 68-70.

Tuesday evening/night: other than opting to linger the
aforementioned slight chance of sprinkles into the first few
hours of the evening period (7-9 pm)...this should be a dry and
uneventful night as the weak middle level disturbance passes through
and south of the local area. Skies should average no more than
partly cloudy...and breezes only 5-10 miles per hour from some variation of
northerly. May have kept lows a touch too mild in a few
spots...but for now have most of the County Warning Area holding up in the 41-44
range...or roughly 3-5 degrees milder than Monday night.

Wednesday/Wednesday night: these 24 hours continue to carry a very
good chance of staying a broad/positively-tilted middle-
upper ridge axis overspreads the Central Plains. Skies should
average mostly sunny...and breezes look to be only around 10 miles per hour
at most. Aimed highs primarily into the 71-73 range...which is a
middle ground between slightly cooler deterministic model
solutions and slightly warmer 00z met/mav guidance.

Thursday daytime-night: confidence remains high in a dry day...and
is fairly high for a dry night as well...although both the
European model (ecmwf)/GFS suggest that the southern fringes of a shortwave trough
passing east across the northern plains could flatten the ridge
just enough to possibly promote a few showers flirting with the
northern County Warning Area Post-midnight. For now this precipitation chance appears too
minor/uncertain to include in the forecast this far out.
Otherwise...this may be the overall-breeziest day out of these 6
days...with sustained southerly speeds probably 15+ miles per hour most
areas. This southerly flow should boost highs a few more
degrees...and have most areas aimed 73-76.

Friday daytime-night: let the weekend parade of fairly "iffy"
shower/thunderstorm chances begin. In the middle-upper
levels...fairly benign quasi-zonal flow looks to rule...but both
the European model (ecmwf)/GFS suggest that by this time there will be just enough
returning instability to combine with subtle/low amplitude
disturbances to spark at least spotty coverage of showers/storms.
Future forecasts may very well have to start these chances Friday
daytime...but will maintain the Friday night mention which appears
a bit more justified. High temperatures aimed 72-76.

Saturday daytime-night: much the same as the preceding 24
hours...except for potentially more instability to kick off a bit
more thunderstorm activity (maybe). Although its a subtle
difference...have slightly higher 30 probability of precipitation focused on Saturday
night versus only 20s during the day. Although convective
influences could obviously change the currently showing
a modest boost in highs into the upper 70s.

Sunday daytime: the same weakly-forced quasi-zonal pattern
continues along with the low-confidence shower/storm
any semblance of a more organized large scale trough remains off
the West Coast. High temperatures very preliminarily prognosticated to be almost
identical to Saturday with upper 70s.


Aviation...(for the 18z kgri/kear tafs through 18z Tuesday afternoon)
issued at 1220 PM CDT Monday Apr 27 2015

Cirrus from thunderstorms in southern Kansas overnight has moved
across the terminal areas. It has been thinning out a little later
this morning and probably will continue to thin through the
afternoon. Northeast winds will have a few gusts this
afternoon...but will diminish overnight.


Gid watches/warnings/advisories...


Short term...Fay
long term...pfannkuch

National Weather Service Glossary of Abbreviations