Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service La Crosse WI
308 PM CDT Tuesday Aug 4 2015

Short term...(this evening through wednesday)
issued at 308 PM CDT Tuesday Aug 4 2015

Latest water vapor satellite imagery indicating upper level trough
over the Hudson Bay/Great Lakes region and upper level ridge over
the northern plains. Latest 20z surface analysis showing high
pressure over eastern Iowa and southern Minnesota providing
mostly/partly sunny skies across the forecast area.

Main forecast concern tonight is the possibility of fog
development in river valleys and parts of central Wisconsin
tonight. Surface ridge builds into eastern Wisconsin and will
provide light winds across the forecast area. Inversion develops
over the forecast area...with dry airmass entrenched over the
region. At this time...patchy fog will be possible in river
valleys and areas of fog possible over parts of central Wisconsin.

High pressure remains in control of the forecast area Wednesday and
provide dry weather and seasonal temperatures.

Long term...(wednesday night through tuesday)
issued at 308 PM CDT Tuesday Aug 4 2015

Focus then turns to Thursday into Friday...the NAM/GFS dprog/dt
indicating slight amplification of upper level ridge and surface
warm front placement further north than previous runs. This would
impact timing of lift/moisture convergence in association with
shortwave trough pushing into northern Minnesota Thursday. Have
reduced precipitation chances and confined small precipitation
chances over the northwest and northern parts of the forecast
area Thursday.

The 04.12z GFS/NAM/ECMWF are in good agreement in increasing
lift/925-850mb moisture transport/convergence into the forecast area
with shortwave trough/surface low/front Thursday night into Friday.
Showers/thunderstorms are likely Thursday night into Friday across
much of the forecast area.

Temperatures Thursday into Friday will be near normal with highs
climbing into the middle 70s to Lower/Middle 80s.

Main forecast concerns are precipitation chances Friday night
through Monday. The 04.12z GFS/ECMWF/Gem are in good agreement in
building upper level ridge over the central and Southern Plains
states through Monday...then amplify ridge over the Rocky Mountains
and northern plains Tuesday. Main differences between the models
are placement and timing of shortwave troughs over-topping the
upper level ridge into the upper Midwest/Great Lakes region.
Based on this...confidence is low on precipitation chances through
Monday. The 04.12z GFS/European model (ecmwf) are in agreement in amplifying upper
level ridge over the northern plains and Rocky Mountains Monday
night and Tuesday. This should allow for dry conditions across the
forecast area.


Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1235 PM CDT Tuesday Aug 4 2015

Areas of valley fog are possible near klse late tonight into early
Wednesday morning. Otherwise...VFR conditions are expected.
Surface high pressure will remain in control this afternoon into
tonight providing quiet weather. Some cirrus is streaming in from
the southwest and a few cumulus have developed mainly north of
Interstate 90 with cloud bases of 4-5 kft. These cumulus will
dissipate early this evening with the loss of daytime heating.
The cirrus should gradually thin late this afternoon and
eventually shift south of the taf sites this evening. VFR
conditions are expected again on Wednesday.


Arx watches/warnings/advisories...


Short term...dtj
long term...dtj

National Weather Service Glossary of Abbreviations