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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
1012 am MDT sun may 24 2015

issued at 955 am MDT sun may 24 2015

Still dealing with flood issues from yesterday...mainly in Logan
County. The upper trough center is over south central Wyoming and
it is not move much. Visible satellite pictures show more sun
getting to the surface than I have seen for quite a few days.
Most of the plains are mostly sunny right now and most of the
foothills were until just recently. It is clouding up pretty
good there now. There is a weak upslope over the plains and the
models keep that going all afternoon into the evening. Certainly
more of the same can be expected this afternoon and evening. It
won't take much rainfall to cause more flooding issues. Agree with
previous forecaster concerning severe weather threat. Just like
yesterday...we just couldn't warm up the 5-10 more degrees f to
make things severe. Will keep the areal Flood Warning north of
Sterling going well into this evening considering the reports we
have been getting.


Short term...(today through tonight )
issued at 327 am MDT sun may 24 2015

Water vapor imagery showing closed upper low over west central
Colorado moving ever so slowly to the east. Models forecast the
low to slowly move east and northeast into eastern Colorado
tonight with moderate southerly flow across the far eastern
plains. Main concern today will be potential flash flooding again
on the eastern plains. Continued southeast low level flow with
surface dewpoints in the upper 40s and lower 50s over far eastern
plains. Storm motions expected to be slower today and potential
for echo training. Given the flooding occurring in portions of
Logan County and significant rainfall...expect more flooding
problems again this afternoon and Sunday evening. Severe weather
threat a bit lower today but still potential for hail/heavy rain
with upwards of 1000j/kg over the plains with 50 dewpoints. Have
opted to go for a Flash Flood Watch over the far northeast plains
this afternoon and tonight. Further west...airmass is slightly
drier with dewpoints mainly lower 40s. See Hydro discussion below
for more.

Long term...(monday through saturday)
issued at 327 am MDT sun may 24 2015

Axis of the upper trough is forecast to pass over eastern Colorado
Monday morning with the 500 mb low center over southeastern Wyoming. Models
show the trough opening up as it swings east-northeastward over the
north-central Great Plains during the day. Flow aloft over the
forecast area still remains moist and marginally unstable at middle-
levels for much of Monday. Meanwhile at the surface...models show a
weak cold front trailing from a surface low somewhere out near the northestern
corner of the state early Monday morning. This front is forecast to
quickly sweep south across the plains in the during the morning hours.
By afternoon models show the northerly low-level flow behind this front
turning into the Front Range which provides additional lift to
generate cloud cover over the area. Although models do not indicate
much in the way of quantitative precipitation forecast with this cloud development...mainly light
rainfall from low top convection over and along the Front Range mountains
during the afternoon. In the high country...should see showers and
possibly a T-storm or two lingering throughout the day with the snow
level lowering to around 9500 feet by mid-afternoon. May even see an
inch or two of new snowfall on the high passes before showers taper
off in the evening as drier air filters in from the northwest.
Temperatures on Monday will remain several degrees below average
with 60s on the plains and upper 40s/50s across the high country.

As the upper trough moves farther away from Colorado...should see
the plains airmass continue to dry and warm on Tuesday with the
boundary layer flow downsloping off the Front Range and Cheyenne Ridge.
The high country will be slower to dry out and warm up with a
continuation of northwesterly middle-level flow. Should see less cloud cover and
notably less shower activity on Tuesday as up upper ridge builds in
from the Great Basin. Expect to see a 2-4 degree f rise in maximum temperatures
with the increase in sunshine. Models show the upper ridge moving
east of the state and the flow aloft becoming southwesterly on Wednesday and
a warming southerly low-level flow on the plains. Wednesday appears warmer
than the day before. However models show a weak shortwave trough
carried along by southwesterly flow aloft passing over the forecast area by the
afternoon which may increase in the likelihood for showers and T-
storms...particularly over higher elevations and along the Wyoming
border. Severe weather risk appears low...but can't rule a stray
hail and/or high wind T-storm or two moving newrd off the Front
Range middle to late afternoon. Could see convection lingering well
into the evening as atmospheric moisture and middle-level instability
gradually increase in advance of the next upper trough carving out
over the eastern Great Basin.

On Thursday...models show this next upper trough deepening some as
it chugs across Colorado over the 36-48 hours...depending on which
model you look at. All models indicate cooler temperatures...greater
cloud cover and an elevated chance for measurable precipitation. Still in
the warm section of this trough precipitation will most likely come from
upright convection/T-storms. So locally heavy rainfall will be
possible based on the elevated precipitable water values given by
the models. Friday looks even wetter and perhaps several degrees cooler
with a moist northeasterly upslope flow developing east of the mountains beneath the
upper trough. GFS is the wettest of the models as it indicates well
over an inch of quantitative precipitation forecast over and along the Front Range by late that
evening. European and Canadian models look much drier as they only
indicate 24-hour rain totals well under an inch and a more progressive
upper trough.

Even by Saturday...GFS still show relatively cool and wet conditions
across the County Warning Area with upslope east of the mountains and the upper trough
still overhead. The European model (ecmwf) indicates a drier and slightly warmer day
with the upper trough shifting east of the state. As usual will use
a blend of the two models for derive a forecast for Friday and Saturday.


Aviation...(for the tafs through 18z Monday morning)
issued at 955 am MDT sun may 24 2015

Weak surface winds will continue well into this evening and they
will have a weak upslope component to them unless altered by
convective outflow for short periods this afternoon and evening.
Gusts above 30 knot are unlikely. Ceilings could get down to
broken/ovc020-bkn/ovc035 once the convection gets going by 20z
through middle evening. Hail is easily possible but it likely would
not exceed 3/8-1/2 inch in size.


Bou watches/warnings/advisories...
Flash Flood Watch through this evening for coz042-044>046-



short term...entrekin
long term...Baker

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