Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260729_1200
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)
=== ===== === ==== ==== === === === ====
Wed 07/29 12Z 0.18 1621  93  92  12 0.00
Wed 07/29 13Z 0.29 1523  89  88  12 0.00
Wed 07/29 14Z 0.31 1523  85  85  12 0.00
Wed 07/29 15Z 0.44 1421  85  86  12 0.01
Wed 07/29 16Z 0.72 1322  85  88  12 0.02
Wed 07/29 17Z 0.77 1323  88  87  11 0.02
Wed 07/29 18Z 0.84 1222  88  83  12 0.01
Wed 07/29 19Z 0.83 1220  85  81  12 0.01
Wed 07/29 20Z 0.79 1121  86  84  12 0.01
Wed 07/29 21Z 0.81 1120  84  87  12 0.01
Wed 07/29 22Z 0.68 1020  81  88  12 0.01
Wed 07/29 23Z 0.66 1021  79  86  12 0.01
Thu 07/30 00Z 0.65 1021  79  84  12 0.01
Thu 07/30 01Z 0.63 1021  80  84  12 0.01
Thu 07/30 02Z 0.58 1020  79  86  12 0.01
Thu 07/30 03Z 0.56 0919  80  89  12 0.01
Thu 07/30 04Z 0.58 0918  84  91  12 0.02
Thu 07/30 05Z 0.58 0818  88  91  12 0.03
Thu 07/30 06Z 0.53 0817  93  91  12 0.04
Thu 07/30 07Z 0.47 0717  90  93  12 0.05
Thu 07/30 08Z 0.45 0617  86  91  12 0.03
Thu 07/30 09Z 0.48 0618  85  91  12 0.01
Thu 07/30 10Z 0.48 0518  87  91  11 0.03
Thu 07/30 11Z 0.47 0519  86  87  11 0.02
Thu 07/30 12Z 0.50 0521  87  87  11 0.01
Thu 07/30 13Z 0.49 0421  88  86  11 0.02
Thu 07/30 14Z 0.44 0420  90  88  11 0.03
Thu 07/30 15Z 0.44 0318  94  88  10 0.05
Thu 07/30 16Z 0.38 0317  96  89  10 0.04
Thu 07/30 17Z 0.37 0217  97  90  10 0.05
Thu 07/30 18Z 0.34 0218  96  87  10 0.07
Thu 07/30 19Z 0.26 0218  95  87  11 0.05
Thu 07/30 20Z 0.21 0218  93  85  11 0.03
Thu 07/30 21Z 0.21 0217  91  79  11 0.01
Thu 07/30 22Z 0.23 0217  92  76  11 0.01
Thu 07/30 23Z 0.26 0217  92  78  11 0.01
Fri 07/31 00Z 0.26 0316  92  80  11 0.00
Fri 07/31 01Z 0.25 0315  92  77  11 0.00
Fri 07/31 02Z 0.26 0315  92  75  11 0.00
Fri 07/31 03Z 0.22 0313  93  79  11 0.00
Fri 07/31 04Z 0.19 0214  95  84  11 0.00
Fri 07/31 05Z 0.20 0214  94  85  11 0.00
Fri 07/31 06Z 0.21 0214  93  81  11 0.00
Fri 07/31 07Z 0.19 0214  93  77  11 0.00
Fri 07/31 08Z 0.13 0114  93  76  11 0.00
Fri 07/31 09Z 0.12 0114  91  74  11 0.00
Fri 07/31 10Z 0.14 0114  91  70  11 0.00
Fri 07/31 11Z 0.13 0114  93  68  11 0.00
Fri 07/31 12Z 0.13 0114  94  67  10 0.00
Fri 07/31 13Z 0.13 0114  94  65  10 0.00
Fri 07/31 14Z 0.16 0113  94  60  10 0.00
Fri 07/31 15Z 0.16 0111  93  58  10 0.00
Fri 07/31 16Z 0.10 0108  94  56  10 0.00
Fri 07/31 17Z 0.04 0006  94  51  11 0.00
Fri 07/31 18Z 0.12 3306  94  53  11 0.00
Fri 07/31 19Z 0.20 3207  93  51  11 0.01
Fri 07/31 20Z 0.23 3209  92  53  12 0.01
Fri 07/31 21Z 0.20 3309  87  52  12 0.00
Fri 07/31 22Z 0.16 3308  84  49  12 0.00
Fri 07/31 23Z 0.16 3309  82  53  12 0.00

Run total areal avg QPF for the greens is: 0.78 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