Predict heat waves / cold snaps

[kylecorry31]

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More research needed, but initial research indicates the following:

Summer (maybe spring/fall - more research needed):

• High pressure: Heat wave

Winter:

• High pressure: Cold snap

Trigger the hot/cold alert.

Open questions:

• Does this apply everywhere?
• How can it tell the difference between a slight change in temperatures vs a worrisome change? What's the threshold for high pressure in this case?
• How long does the high pressure need to be in place for there to be a heat wave? Can this be determined through tendency?
• Should it show an alert notification (similar to the storm alert)?
• How far in advance can it tell (normal pressure + tendency increasing = will be high pressure soon)?
• Should this count as its own weather condition or just an alert?
• Should a note be displayed on the historic temperature list items?
• Does it matter if it just gives a heat alert vs a heat wave? (probably not)

Precursor to #1586