Scientific Forecaster Discussion

NWS Discussion
			
				

Area forecast discussion 
National Weather Service Las Vegas Nevada 
946 am PDT Sat may 25 2013 


Synopsis...a dry southwest flow will persist over the region 
through Memorial Day. Locally breezy to windy conditions will 
develop each afternoon with temperatures slightly below normal. A 
low pressure system is expected to move into Nevada Tuesday bringing 
a chance of showers and thunderstorms and much cooler temperatures 
to the region. 
&& 


Update...a broad trough over the western states will continue 
through the Holiday weekend and into early next week. A series of 
disturbances will brush across northern Nevada today and again 
Sunday...before trough digs into the southern Great Basin on 
Tuesday. A dry southwest flow will persist through Monday leading to 
breezy to locally windy conditions. Believe a red flag warning is 
not justified across Mohave County today but will monitor winds 
closely just in case. Conditions looks very similar for Sunday so at 
this time do not anticipate any new products being issued. 


Did adjust sky and wind grids some with the morning update. 
&& 


Aviation...for McCarran...southwest winds 13-20kts through the 
afternoon hours with gusts around 25kts. Few-scattered high clouds at or above 25k 
feet. Similar winds expected on Sunday but likely a knots or two 
lighter. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...south to southwest winds 12-18 kts the rest of the 
morning then increasing to 15-25kts by middle day. Stronger gusts of 30 
to 35kts are possible in the vicinity of kigm and across the 
northwest plateau of Mohave County. Winds will be similar on Sunday 
but marginally weaker by a couple kts. Scattered high clouds at or above 25k feet 
at times. 
&& 


Previous discussion... 
250 am PDT Sat may 25 2013 


Short term...today through Monday night...the low pressure system 
which has been over the Pacific northwest the past several days will 
continue over the region through Sunday before lifting to the 
northeast late Sunday. Another low is then forecast to drop south on 
Memorial Day and move into the County Warning Area late Monday night. The short 
range models are coming more inline with this second system...but 
the European model (ecmwf) continues to be a little slower and deeper than the 
GFS/NAM. Thus have trended towards a compromise for the Monday night 
period. The result is that continued dry southwest flow will remain 
over the region today through much of Memorial Day...before 
increasing clouds are seen Monday night County Warning Area wide with a chance of 
showers over the southern Sierra by Tuesday morning. 


The main concern during the short term will continue to be breezy to 
windy southwest winds during the afternoons and early evenings 
across much of the region. The strongest winds are likely to be seen 
across Mohave County and the extreme western portion of the Mojave 
Desert with fire weather concerns being the main impact. However 
will need to monitor the winds as local gusts may reach into 
advisory levels on Sunday and Monday afternoon. 


Daytime temperatures will continue to be 3 to 5 degrees below normal 
through the period. 


Long term...Tuesday through Friday...the 00z European model (ecmwf) trended weaker 
than the previous run with energy moving into the Great Basin 
Tuesday while the GFS remained progressive and dry. In 
response...associated parameters were adjusted to account for the 
weaker...more progressive European model (ecmwf) solution. Temperatures were raised 
slightly...probability of precipitation were lowered across mainly the southern County Warning Area with 
adjustments to timing and precipitation location made further north. Quantitative precipitation forecast 
amounts were kept light based on limited available moisture and the 
progressive nature of the system. Models bring more shortwave energy 
across northern Nevada Wednesday which could increase winds and 
result in a few showers across the north. The European model (ecmwf) maintains a 
northwest flow across the region Thursday and Friday with additional 
vorticity energy moving through the area. The GFS and Gem are more zonal 
with impacts limited to areas well north of the area. 
&& 


Fire weather...the Pacific low pressure area which has been over 
the Pacific northwest for the past several days will continue over 
the area through Sunday. This will continue to result in breezy 
to locally windy conditions during the afternoon/early evenings 
across the district. Local red flag conditions will likely be 
seen...especially across Mohave County Arizona and the western 
portion of the Mojave Desert and will need to monitor for winds 
becoming more widespread than current thinking. In addition very dry 
conditions will continue with minimum relative humidity values 
lowering to below 10 percent across much of the district each 
afternoon...with only poor recoveries overnight...especially in the 
lower deserts. 


A change is expected to take place on Tuesday however as another low 
pressure area begins to drop south and across the region. This 
system is expected to bring cooler temperatures to the district 
along with a slight chance of showers/possible thunderstorms to the 
mountains Tuesday afternoon...while local gusty winds will continue 
to be seen. 
&& 


Vef watches/warnings/advisories... 
Nevada...none. 
Arizona...none. 
California...none. 
&& 


$$ 


Update...Pierce 
aviation...czyzyk 
previous discussion...Jensen/Salmen 


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