Is there a NOTAM code for solar eclipse?
For the solar eclipse of March 20, 2015, I found this example below, seems like it's the opposite of a warning.


  E) A SOLAR ECLIPSE WILL TAKE PLACE ON THE 20TH OF MARCH.
  SPECIAL ROUTES HAVE BEEN DEFINED FOR FLIGHTS PLANNING TO VIEW THE ECLIPSE.
  THE ROUTES ARE DEFINED AS FOLLOWS:
  
  (...)
  
  ANY ADDITIONAL REQUESTS FOR A SOLAR ECLIPSE PROFILE SHALL BE SENT TO REYKJAVIK OACC SHIFT MANAGER, SEE CONTACT INFO BELOW. SOLAR ECLIPSE FLIGHTS WILL BE GIVEN PRIORITY DURING THE ECLIPSE.
  OTHER FLIGHTS MAY EXPECT A REROUTE AND OR LEVEL CHANGE FOR SEPARATION PURPOSES.


Regarding the temperature drop, from NASA:


  Because the patch of the shadow travels faster than the speed of sound, weather systems will only be affected very locally directly under the instantaneous footprint of the eclipse. The main effect is in the "radiant heating" component which goes away suddenly at the moment of eclipse and produces a very fast temperature decrease. If the wind is blowing, your body probably exaggerates, by evaporative cooling, how large the actual temperature swing actually is.


Due to the Earth's geometry, the shadow's speed differs from location to location, the slowest equates to Mach 2.2 at 50,000 feet for an F-15 to fly along.

Even for that F-15 in constant complete darkness, every instance is a new darkness. Some sources mention the drop at the surface being 3°C (5°F), but it looks like it's not a thoroughly studied field (impact of solar eclipses on local weather).