|Fig 1--GOES-W IR satellite image from 1030Z Nov 4th, 2010|
This looks like a powerful storm, but just how severe is it at the surface? It's difficult to get good obsevations in Alaska, mostly because there's a lot of open water and even on land the populated areas are very sparse. One way we can try to get a more cohesive set of measurements is to use satellite-derived winds. One simple way to do this is to identify certain cloud features on a satellite image and then see how far they move over a given time. By estimating the elevation off the ground (or ocean) of these cloud features, we can get an estimate of the winds at that level. However, since clouds have depth, they tend to cover multiple levels of height. Therefore, the best we can do is guess at the wind speeds within a layer. An example of one of these products can be seen here:
|Fig 2--GOES W Pacific region IR-derived winds, 1445Z, Nov 4th, 2010. Yellow indicates 700-1000mb, cyan indicates 400-699mb, and red indicates 100-399mb.|
Anyhow, we can see that in the Gulf of Alaska that there are several low-level (yellow) wind barbs in the 30-35 knot range, which isn't too extreme but still could pack quite a punch. It's clear that there's probably a lot of cloud cover and maybe precipitation associated with this cyclone as per the IR image (fig 1). So how is Alaska reacting to this storm?
Here's the current radar (1742Z) from Anchorage (PAHG):
|Fig 4--PAHG BREF1 Radar image from 1742Z, Nov 4th, 2010|
.TODAY...RAIN AND SNOW SHOWERS CHANGING TO ALL SNOW. SNOW ACCUMULATION 2 TO 4 INCHES. HIGHS IN THE LOWER TO MID 30S. SOUTH WIND TO 15 MPH WITH LOCAL GUSTS TO 25 MPH.
So we can see that they are indeed calling for rain and snow and some wind. Why isn't this such a big deal? Two big reasons--
1) Most of Alaska's major populated areas are not located in areas immediately facing the open Pacific Ocean. In fact, The coastal mountain ranges including the Aleutians, the Kenai, the Chugach and the Wrangell-St. Elias Mountains all provide some measures of shelter to even "coastal" cities and towns. Most are on some sort of gulf or inlet that actually puts the city pretty far inland from the open water. Such mountain ranges can also force a lot of lift and consequently lots of precipitation on the windward, ocean-ward side and leave much drier conditions on the leeward side.
2) It's Alaska. 2-4 inches of snow is normal. Nothing to be alarmed about...
So, there you have it. It should be clear that just because a storm looks impressive on satellite (or radar..) doesn't meant that the storm necessarily must be extraordinarily crazy or record breaking. Alaska has its share of impressive-looking storms and some do arrive with more impressive precipitation and winds than most. Therefore forecasters up there must be very vigilant and proactive to get warnings out there. However, like we saw with the satellite-derived winds and the squashed images, getting good weather data in Alaska is rather difficult. It just makes forecasting that much harder, even if the weather can get somewhat beautiful (fig 1).