Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260312_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 03/12 00Z 0.43 2043  83  89  11 0.00
Thu 03/12 03Z 0.83 2340  94  81  10 0.05
Thu 03/12 06Z 0.66 2136  97  84  11 0.05
Thu 03/12 09Z 1.74 2633  98  95   5 0.17
Thu 03/12 12Z 0.87 2731  84  70  -3 0.07
Thu 03/12 15Z 1.75 2828  85  14  -9 0.00
Thu 03/12 18Z 1.77 2925  87  30 -12 0.00
Thu 03/12 21Z 4.93 3023  85  44 -14 0.00
Fri 03/13 00Z 1.75 3025  86  39 -14 0.00
Fri 03/13 03Z 2.93 3028  91  52 -14 0.00
Fri 03/13 06Z 1.19 3024  91  47 -14 0.00
Fri 03/13 09Z 0.88 2923  88  59 -13 0.00
Fri 03/13 12Z 0.64 2818  85  11 -12 0.00
Fri 03/13 15Z 0.30 2309  69   5 -10 0.00
Fri 03/13 18Z 0.15 1817  54  77  -9 0.00
Fri 03/13 21Z 0.07 1730  91  87  -8 0.03
Sat 03/14 00Z 0.33 1937  92  82  -8 0.05
Sat 03/14 03Z 0.57 2038  94  75  -6 0.00
Sat 03/14 06Z 0.68 2135  94  80  -5 0.00
Sat 03/14 09Z 1.33 2333  97  44  -7 0.00
Sat 03/14 12Z 2.67 2435  92  23 -10 0.01
Sat 03/14 15Z 4.93 2533  87  47 -11 0.00
Sat 03/14 18Z 17.10 2734  83  75 -11 0.00
Sat 03/14 21Z 4.07 2534  87  48 -11 0.00
Sun 03/15 00Z 3.35 2934  86  37 -13 0.00
Sun 03/15 03Z 1.15 3031  70   7 -13 0.00
Sun 03/15 06Z 0.40 3123  40  12 -10 0.00
Sun 03/15 09Z 0.27 3117  29   6  -9 0.00
Sun 03/15 12Z 0.17 3009  20  14  -8 0.00

Run total areal avg QPF for the greens is: 0.43 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1