Weather

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fxus65 kpub 061328 aaa 
afdpub 


Area forecast discussion...updated 
National Weather Service Pueblo Colorado 
728 am MDT Monday Oct 6 2008 


Update... 


Updated forecast to trim probability of precipitation out of most of the I-25 corridor to 
follow latest radar trends. -Kt 


&& 


Previous discussion... /issued 413 am MDT Monday Oct 6 2008/ 


Short term... 
(today and tonight) 


Upper trough ejecting into the Central Plains is still prognosticated to 
close off across the panhandles and western Kansas later this morning. Surface 
low center is positioned across NE nm with cold front having cleared 
all but the southeast corner of the state so far. Band of wrap 
around precipitation has spread southward across the eastern plains 
overnight...and nam12 shows this axis shifting south and eastward 
through the morning as the upper low pulls away from the region. Thus 
will keep some likely probability of precipitation mainly east of klhx through the 
morning...with precipitation ending for most of the area by afternoon as drier air 
moves in. Still quite a bit of orographic cloudiness pinned up 
along the northwest facing slopes of the Continental Divide in latest fog products. 
Some of the mountain observation sites reporting light snow...but check of myp 
web cam so far appears to be more of a visible restriction rather than 
falling snow. Will hang on to some isolated probability of precipitation along the northwest 
facing slopes of the central mts this morning. Expect gusty north 
winds through the morning across the plains...with winds diminishing 
this afternoon as surface pressure gradient relaxes. Cooler day for 
most areas today...especially across the east. With more sunshine and middle 
level warm air advection moving in from the west...southwest and central mts may end 
up being a couple degrees warmer than yesterday. 


For tonight...cool air mass over the area in wake of today's 
system...and with clear skies...light winds...and dew points falling 
into the upper 20s and lower 30s...set up certainly seems favorable 
for frost development. Driest airmass (and area with best potential 
for frost) appears to be along the I-25 corridor. Farther east GFS 
and NAM keep surface dew points in the upper 30s along the eastern 
border. Surface pressure gradient pretty weak...so don't think that 
drainage flow will be sufficient to offset development of strong 
surface inversions. In fact...winds through the surface to 700 mb layer are 
around 5 kts or less in both the NAM and GFS. Thus think temperatures 
could dip to near or slightly above freezing along the I-25 corridor 
late tonight through tomorrow...and will issue a frost advisory for 
this region. Within this area...the most likely spots to see frost 
will be Palmer Divide and in the Pueblo frost pocket along the 
Arkansas River valley. Its possible that the frost advisory may need 
to be expanded eastward a bit...but given the possibility that dew 
points may stay too high out east...will leave this for the next 
shift to assess. Interior mountain valleys will also experience a cold 
night...however the San Luis valley has already experienced a hard 
freeze earlier this season...and we are beyond the typical end of 
the growing season (oct 1st) for that region...so no highlight 
should be necessary. -Kt 


Long term... 
(tuesday through sunday) 


.Warm days and cool nights Tue-Thu... 
.unsettled weather possible Fri-sun... 


Tuesday through Thursday...westerly flow aloft should dominate 
the weather pattern. Relatively warm days and cools nights should 
be in the offing with the forecast challenge being an exercise in 
temperature forecasting across complex terrain. Potential for some 
breezy conditions across the high terrain Wednesday and 
Thursday...mainly afternoon. 12km NAM-WRF suggests a weak cold 
front to move through eastern Colorado late Wednesday into Thursday 
morning with little impacts. 00z/06 GFS is now much faster 
bringing in the lead trough and associated weather for late 
Thursday...somewhat similar to some of the old European model (ecmwf) runs. The 
00z/06 European model (ecmwf) run no longer portrays this scenario. Uncertainty 
remains...so will maintain the Thursday forecast. 


Friday through Sunday...much more forecast uncertainty for these 
forecast periods. Medium range models suggest "something" is 
coming through the central Rocky Mountains...but as usual the 
devil is in the details. GFS and European model (ecmwf) are now at odds with the 
timing...strength...and evolution of the weather system. GFS 
continues to support a more progressive "open wave" system while 
the European model (ecmwf) has switched back to the Mammoth low pressure system 
over the Great Basin. If the GFS is correct then there would be a 
better chance for precipitation and much colder temperatures. With 
700mb temperatures around -8c to -12c...high temperatures across 
southeastern Colorado could very well only be in the 40s. Now...if the 
00z/06 European model (ecmwf) is more correct...then the associated upper level jet 
streak is directly over Colorado...which doesn't Bode well for precipitation. 
The weather system's "dry slot"(700-300mb relative humidity around 15%) will be 
across much of Colorado late Sat-sun and 700mb temperatures will be 
warmer than what the GFS portrays. Obviously...will maintain the 
current deterministic forecast given the many different solutions 
that could occur in these forecast periods. 17 


Aviation... 


Gusty north winds expected across the kcos and kpub taf sites this 
morning. Middle deck of VFR ceilings along the I-25 corridor should 
dissipate by afternoon. Farther east...scattered to numerous showers 
and thunderstorms will continue through the morning producing MVFR 
to local IFR ceilings...along with locally heavy rain. These will shift 
south and east of the area by afternoon. IFR to LIFR mountain obscurations 
will linger along the northwest facing slopes of the Continental Divide through the 
morning with clearing skies in the afternoon. Clear skies and light 
diurnally driven winds expected tonight. -Kt 


&& 


Pub watches/warnings/advisories... 
frost advisory from midnight tonight to 9 am MDT Tuesday for 
coz083>088. 


&& 


$$ 


31/17 

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