KMDT/KCXY · Fog + Visibility

Fog & Visibility

Susquehanna River fog climatology · Both eras · IEM hourly
MDT Dense Fog (Early)
0.8%
% hourly obs 1948-65
CXY Dense Fog (Early)
0.7%
MDT 14% more fog hours
MDT Dense Fog (Modern)
0.1%
ASOS era — less reported
Foggiest Month
Nov
River cooling drives fog
Low-Vis (≤1mi) Peak
Nov
~6% hours at MDT early era
Dense Fog Frequency (% hrs vis <0.25mi) — Both Eras
Low Visibility (% hrs vis ≤1mi) — Both Stations Both Eras
MDT vs CXY Fog Scatter — Each point = one month (hover for label)
Mean Hourly Visibility by Month — Both Stations Both Eras

Key Findings

01
MDT is consistently foggier than CXY in every month. The Susquehanna River produces radiative and evaporative fog when water temperature exceeds air temperature — most prominent in autumn as the river cools slowly.
02
Dense fog declined dramatically between eras — MDT 0.8% → 0.1%. This reflects both ASOS forward scatter sensor changes vs human observation and real improvements in fog reporting methodology.
03
November is the foggiest month at MDT in both eras. River retains summer heat well into autumn while air temperatures drop rapidly, maximizing surface-to-air temperature differential that drives fog over the floodplain.
04
CAD relevance: During cold air damming events NE flow advects moisture into the valley. MDT's floodplain position means fog persists longer than at CXY during these events — a CAD signature detectable in the hourly visibility record.