Local Forecast
Weather Wars: 7 Day Forecast Battle
Days Mon Tue Wed Thu Fri Sat Sun
Lee C. -- -- -- -- -- -- --
John Y. -- -- -- -- -- -- --
Temperature Verification
Days Mon Tue Wed Thu Fri Sat Sun
Temps -- -- -- -- -- -- --

Risk of Snow Showers tomorrow, cold for Friday

By Lee Carlaw On Wednesday, January 23, 2008 At 5:19 PM
Current Weather:
Temperatures currently in the lower 40s should drop into the mid 20s overnight under mainly clear skies and light winds in and around the Beltway. Farther to the north and west, temperatures are presently in the mid to upper 30s, and should fall into the upper teens overnight.

Forecasts For the Next Few Days:


By 8 or 9 AM tomorrow, clouds should begin streaming in from the west, as energy associated with a tiny pocket of mid and upper level energy slides east from the Midwest. High temperatures tomorrow will hover in the lower to mid 30s in and around DC, which will support a few snow showers, which may develop during the late morning and into the late afternoon hours. Some minor snow accumulation is possible on grassy and elevated surfaces, but most roadways should remain snow-free due to above-freezing road temperatures.

Probability of Snow: 40%

Image at right: NAM forecast precipitation for Thursday afternoon showing the possibility of some light snow showers around the metro region. Image courtesy of the Penn State E-Wall

Cold, Canadian air is expected to pour into the region overnight Thursday as a cold front sweeps through the Mid Atlantic. Temperatures early Friday morning will range from 15 around Hagerstown and surrounding areas, to near 20 near Washington, D.C.

Clouds should scour out by mid morning, leaving us with mainly sunny to skies. High temperatures will be in the upper 20s and lower 30s.

Clouds will increase late Friday night and into Saturday morning as a very weak upper level disturbance rotates through the region. At this point, there does not appear to be enough lift to get any precipitation over the mountains. Temperatures will hover around 40.

Paying Attention to What the Forecaster Actually Says:
With the recent forecasts of snow in the metro region, it has gotten to me when people ask me, "hey, the weather channel said there was supposed to be snow last night. How come there was none/How come it didn't stick?"

It seems incredible to me that, with all the precision and time forecasters put into their work, the vast majority of the public really doesn't pay attention to some of the crucial details. Here's a portion of the text forecast for Montgomery county for Thursday from the National Weather Service:

Seems simple enough, right? Now, take a quick look at the image to the right. It's The Weather Channel's forecast for Thursday. If it DIDN'T snow at all tomorrow, I would bet that most people would say, "the meteorologists got it wrong again. Where was the snow??"

Very few public viewers actually take the time to read the forecast text. Notice that little percentage at the bottom? In the NWS text forecast, this percentage is 40%, and in The Weather Channel's it's 30%. These are known as Probabilities of Precipitation.

Most people think of POP as the percentage of getting precipitation on that day. That, unfortunately, is only one part of the formula. POP is based on two things:

1) The probability that any precipitation will fall in the time period and
2) The predicted areal coverage if precipitation actually develops

So take this hypothetical situation (it would more than likely never happen, but what the heck):
Washington, D.C. records a POP of 20% for 100 consecutive days. If this POP were accurate over the long term, then Washington should have experienced some type of precipitation for 20 of those 100 days (not a great number, right?) The likelihood of precipitation being recorded when the POP is 20% is extremely low.

So, the next time you read or hear a forecast, it would be wise to also look or listen for the Probability of Precipitation. Weather isn't exactly and exact science.

for this post

Anonymous ice Says:

Pretty nice info... But I think it is outdated... Hope you could update this in the future... :) Nice blog...

Anonymous Anonymous Says:

hello... hapi blogging... have a nice day! just visiting here....

Anonymous Anonymous Says:

Download Forum Poster V3 3.0 at FileAfro.com


Anonymous Anonymous Says:

hello... you may submit this blog to my webBlog Directory, keyworddir.info.. have a nice day!

Keyword Directory

Anonymous Anonymous Says:

Watch Natsha Naked!

Anonymous Anonymous Says:

hi.. just dropping by here... have a nice day! http://kantahanan.blogspot.com/

Blogger JanuskieZ Says:

Hi... Looking ways to market your blog? try this: http://bit.ly/instantvisitors

Anonymous Anonymous Says:

Who knows where to download XRumer 5.0 Palladium?
Help, please. All recommend this program to effectively advertise on the Internet, this is the best program!

Anonymous Micah Says:

This is a great post.. Very informative... I can see that you put a lot of hard work on your every post that's why I think I'd come here more often. Keep it up! By the way, you can also drop by my blogs. They're about Vegetable Gardening and Composting. I'm sure you'd find my blogs helpful too.


Leave a Reply

Contact Us
wxdude1990 (at) yahoo.com jyarsh381 (at) hotmail.com


Useful NOAA Weather Links
Local Weather Service Office
Hydrometeorological Prediction Center
Storm Prediction Center (Severe Weather)
National Hurricane Center

Watches, Warnings, Advisories

Numerical Weather Models
NCEP Models (good selection)
PSU E-Wall
25 km WRF model (Hi-Res)
Earl Barker's Model Page
Ensemble MOS data (Washington, DC)

Radar and Satellite
Local Radar

PSU E-Wall Satellite
Local NWS radar
ABC Radar
FOX Radar
NBC Radar

Other Weather Blogs
USA Today's The Weather Guys
The Weather Underground blog
Foot's Forecast
Weather Talk Radio
Eastern US Weather Forum

Other Blogs
BayArea Kicks

Enter your e-mail to subscribe:

Personal Blogs - Blog Top Sites


Personal blogs
Top Blogs

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.