Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20261103_0600
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)
=== ===== === ==== ==== === === === ====
Tue 11/03 06Z 0.47 2813  59  88   9 0.00
Tue 11/03 09Z 0.37 2710  57  86   9 0.00
Tue 11/03 12Z 0.39 2411  63  91   9 0.00
Tue 11/03 15Z 0.44 2314  63  95   9 0.00
Tue 11/03 18Z 0.54 2217  72  94   8 0.00
Tue 11/03 21Z 0.61 2324  89  88   9 0.01
Wed 11/04 00Z 0.61 2524  93  77  10 0.02
Wed 11/04 03Z 0.77 2726  85  67  11 0.00
Wed 11/04 06Z 0.93 2626  74  53  11 0.00
Wed 11/04 09Z 0.93 2627  70  66  11 0.00
Wed 11/04 12Z 1.00 2628  69  71  11 0.00
Wed 11/04 15Z 0.76 2625  66  78  12 0.00
Wed 11/04 18Z 0.53 2519  62  59  13 0.00
Wed 11/04 21Z 0.47 2417  65  49  13 0.00
Thu 11/05 00Z 0.55 2520  68  49  12 0.00
Thu 11/05 03Z 0.43 2419  52  52  13 0.00
Thu 11/05 06Z 0.38 2322  45  51  14 0.00
Thu 11/05 09Z 0.47 2329  50  48  14 0.00
Thu 11/05 12Z 0.48 2231  64  40  13 0.00
Thu 11/05 15Z 0.65 2234  97  94  11 0.00
Thu 11/05 18Z 0.65 2329  93  65  11 0.05
Thu 11/05 21Z 0.70 2327  82  12  10 0.00
Fri 11/06 00Z 0.82 2330  91  12   9 0.00
Fri 11/06 03Z 0.71 2329  89  30  10 0.02
Fri 11/06 06Z 0.78 2621  88  14   6 0.01
Fri 11/06 09Z 0.58 2617  87  26   5 0.00
Fri 11/06 12Z 0.45 2514  85  30   4 0.00
Fri 11/06 15Z 0.28 2310  80  36   5 0.00
Fri 11/06 18Z 0.24 2208  82  36   5 0.00

Run total areal avg QPF for the greens is: 0.11 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