Scientific Forecaster Discussion
fxus63 koax 210440
Area forecast discussion
National Weather Service Omaha/valley NE
1140 PM CDT Fri Sep 20 2019
Short term...(tonight through monday)
issued at 351 PM CDT Fri Sep 20 2019
Water vapor imagery this afternoon showing large scale flow aloft
consisting of a large high pressure dome situated over the eastern
half of the Continental U.S. Along with a well amplified longwave trough
across the western half and an embedded circulation centered over
the great basic.
Meanwhile surface low pressure was centered over ND with a strong
thrust of Gulf moisture into the Central Plains. Morning precipitable water plow
revealed 1.4" at koax and 1.6" at ktop. Latest obs were showing, for
the most part, dew points around 70 over the County Warning Area.
Models are in agreement large scale pattern will become more
progressive in nature beginning tonight when Great Basin upper low
gets ejected and moves toward the western Dakotas late tonight. With
this, synoptic scale lift increases over the region in conjunction
with associated cold front approaching the County Warning Area. Models are in decent
agreement showing precip breaking out within the warm sector ahead
of the front early Saturday morning. The boundary is progged to
become quasi-stationary Saturday afternoon and take on an
orientation from east-west over the southern County Warning Area.
With near stagnant differential divergence acting as a forcing
mechanism, conditions will become quite favorable for heavy
rainfall Saturday night into early Sunday morning. As of now,
models are pointing to the County Warning Area for possible excessive rainfall
where precip efficiency will be most prevalent. Pws approximately
over 150% of normal will phase with deep low level warm cloud
layer and Max Omega. Precip activity south of I-80 should be
coming to a gradual close through early Sunday morning. As of now,
rainfall totals over 2 inches appear possible over
Nemaha/Pawnee/Richardson counties in NE and Page County in Iowa.
Thus, a Flash Flood Watch will be in effect Saturday night into
early Sunday morning over portions of southeast NE and southwest
Increasing heights building in from the west will result in very
pleasant conditions Sunday afternoon into Monday.
Highs on Saturday will be in the low 80s. On Sunday and Monday
highs will be in the 70s.
Long term...(monday night through friday)
issued at 351 PM CDT Fri Sep 20 2019
Precip chances in the extended periods will come in part to several
impulse associated with the next system digging down the western
states and eventually bottoming out over the southwestern Continental U.S..
the GFS and ecm differ slightly with timing of main circulation
into the Central Plains. GFS progs in into the County Warning Area early Friday
morning while the ecm brings it through Friday afternoon.
Highs on Tuesday will be in the upper 80s. Highs in the low/mid 70s
then Wednesday through Friday.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1125 PM CDT Fri Sep 20 2019
Breezy southerly winds are expected to continue into Saturday
morning. Current MVFR ceilings will continue to decrease to IFR
early Saturday morning. Additionally, a few spotty showers may be
possible at Oma and lnk Saturday morning. Otherwise ceilings
should improve to VFR after sunrise. Chances for showers and
thunderstorms may be possible again late in the taf period at Oma
and lnk but confidence is low, with higher chances remaining south
of the taf sites, so it has been left out of this round of tafs.
NE...Flash Flood Watch from Saturday evening through Sunday morning
Iowa...Flash Flood Watch from Saturday evening through Sunday morning