Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260729_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)
=== ===== === ==== ==== === === === ====
Wed 07/29 06Z 0.08 1715  93  96  13 0.00
Wed 07/29 07Z 0.15 1619  93  94  13 0.00
Wed 07/29 08Z 0.18 1621  93  93  13 0.01
Wed 07/29 09Z 0.23 1622  93  91  13 0.01
Wed 07/29 10Z 0.33 1526  91  91  13 0.01
Wed 07/29 11Z 0.39 1528  90  88  13 0.01
Wed 07/29 12Z 0.37 1528  86  85  13 0.01
Wed 07/29 13Z 0.34 1524  86  81  13 0.01
Wed 07/29 14Z 0.40 1422  84  71  13 0.00
Wed 07/29 15Z 0.58 1322  89  69  13 0.00
Wed 07/29 16Z 0.76 1322  91  66  12 0.01
Wed 07/29 17Z 0.93 1322  93  69  12 0.01
Wed 07/29 18Z 0.79 1321  94  72  12 0.01
Wed 07/29 19Z 0.74 1220  94  74  12 0.01
Wed 07/29 20Z 0.69 1220  93  79  12 0.02
Wed 07/29 21Z 0.62 1120  91  79  12 0.04
Wed 07/29 22Z 0.58 1121  86  79  12 0.01
Wed 07/29 23Z 0.55 1120  81  79  13 0.00
Thu 07/30 00Z 0.51 1019  80  80  13 0.01
Thu 07/30 01Z 0.51 0919  81  85  13 0.01
Thu 07/30 02Z 0.51 0919  79  90  12 0.01
Thu 07/30 03Z 0.49 0918  76  92  13 0.00
Thu 07/30 04Z 0.47 0817  76  94  13 0.00
Thu 07/30 05Z 0.41 0715  78  93  12 0.00
Thu 07/30 06Z 0.40 0615  78  94  12 0.01
Thu 07/30 07Z 0.44 0616  82  93  12 0.02
Thu 07/30 08Z 0.46 0617  84  93  11 0.02
Thu 07/30 09Z 0.45 0616  87  91  11 0.02
Thu 07/30 10Z 0.44 0517  86  89  11 0.02
Thu 07/30 11Z 0.43 0517  85  89  11 0.02
Thu 07/30 12Z 0.40 0417  83  89  11 0.01
Thu 07/30 13Z 0.42 0418  79  89  11 0.01
Thu 07/30 14Z 0.37 0418  75  89  12 0.00
Thu 07/30 15Z 0.39 0318  80  90  11 0.00
Thu 07/30 16Z 0.65 0217  83  86  11 0.00
Thu 07/30 17Z 0.60 0217  86  90  11 0.00
Thu 07/30 18Z 0.71 0318  89  95  11 0.01
Thu 07/30 19Z 0.53 0319  88  96  11 0.01
Thu 07/30 20Z 0.47 0320  88  94  11 0.01
Thu 07/30 21Z 0.44 0320  85  86  11 0.01
Thu 07/30 22Z 0.46 0419  87  80  11 0.00
Thu 07/30 23Z 0.46 0419  85  78  11 0.00
Fri 07/31 00Z 0.44 0418  84  80  11 0.00
Fri 07/31 01Z 0.40 0517  86  77  11 0.00
Fri 07/31 02Z 0.32 0414  87  72  11 0.00
Fri 07/31 03Z 0.26 0313  86  73  11 0.00
Fri 07/31 04Z 0.21 0312  87  74  11 0.00
Fri 07/31 05Z 0.16 0212  87  72  11 0.00
Fri 07/31 06Z 0.15 0212  86  66  11 0.00
Fri 07/31 07Z 0.15 0113  87  62  11 0.00
Fri 07/31 08Z 0.16 0114  89  60  11 0.00
Fri 07/31 09Z 0.17 0215  89  55  11 0.00
Fri 07/31 10Z 0.20 0215  87  52  11 0.00
Fri 07/31 11Z 0.17 0214  87  52  11 0.00
Fri 07/31 12Z 0.13 0113  88  55  11 0.00
Fri 07/31 13Z 0.13 0112  90  57  11 0.00
Fri 07/31 14Z 0.13 0210  91  59  11 0.00
Fri 07/31 15Z 0.10 0108  92  59  11 0.00
Fri 07/31 16Z 0.05 0007  92  58  11 0.00
Fri 07/31 17Z 0.08 3507  92  56  11 0.00

Run total areal avg QPF for the greens is: 0.37 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