Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260617_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 06/17 06Z 0.36 2310  76  58   9 0.00
Wed 06/17 07Z 0.37 2210  76  59   9 0.00
Wed 06/17 08Z 0.31 2209  74  59   9 0.00
Wed 06/17 09Z 0.25 2109  71  57   9 0.00
Wed 06/17 10Z 0.23 2108  70  55   9 0.00
Wed 06/17 11Z 0.22 2109  70  53   9 0.00
Wed 06/17 12Z 0.18 2008  70  51   9 0.00
Wed 06/17 13Z 0.16 1908  70  58   9 0.00
Wed 06/17 14Z 0.16 1807  71  68   9 0.00
Wed 06/17 15Z 0.47 1707  71  75  10 0.00
Wed 06/17 16Z 0.51 1809  73  73  10 0.04
Wed 06/17 17Z 0.49 1809  72  66  10 0.04
Wed 06/17 18Z 0.34 1810  74  68  10 0.02
Wed 06/17 19Z 0.80 1911  73  73  10 0.02
Wed 06/17 20Z 0.33 1909  72  72  10 0.02
Wed 06/17 21Z 0.12 1710  71  67  11 0.00
Wed 06/17 22Z 0.22 1812  71  68  11 0.00
Wed 06/17 23Z 0.18 1814  71  65  11 0.00
Thu 06/18 00Z 0.15 1815  74  57  11 0.00
Thu 06/18 01Z 0.33 1917  77  50  11 0.00
Thu 06/18 02Z 0.34 1919  82  44  11 0.00
Thu 06/18 03Z 0.33 2021  85  42  11 0.00
Thu 06/18 04Z 0.29 2019  86  64  11 0.00
Thu 06/18 05Z 0.25 2018  83  58  11 0.00
Thu 06/18 06Z 0.23 1920  82  58  11 0.00
Thu 06/18 07Z 0.26 1923  86  70  11 0.00
Thu 06/18 08Z 0.18 1924  88  86  11 0.01
Thu 06/18 09Z 0.18 1927  89  81  11 0.02
Thu 06/18 10Z 0.10 1828  89  77  11 0.02
Thu 06/18 11Z 0.13 1830  91  89  12 0.02
Thu 06/18 12Z 0.08 1834  87  93  13 0.01
Thu 06/18 13Z 0.05 1838  86  81  13 0.02
Thu 06/18 14Z 0.07 1742  88  86  14 0.02
Thu 06/18 15Z 0.06 1844  95  96  13 0.04
Thu 06/18 16Z 0.09 1842  96  98  13 0.10
Thu 06/18 17Z 0.16 1840  98  90  13 0.22
Thu 06/18 18Z 0.22 1937  97  75  14 0.09
Thu 06/18 19Z 0.30 1933  96  71  14 0.05
Thu 06/18 20Z 0.51 2029  96  72  14 0.10
Thu 06/18 21Z 0.99 2326  93  82  14 0.16
Thu 06/18 22Z 1.10 2426  85  38  13 0.09
Thu 06/18 23Z 1.40 2425  91  41  12 0.00
Fri 06/19 00Z 1.55 2429  91  58  12 0.02
Fri 06/19 01Z 1.75 2533  92  72  10 0.06
Fri 06/19 02Z 1.60 2533  90  70   9 0.02
Fri 06/19 03Z 1.49 2533  94  69   8 0.01
Fri 06/19 04Z 1.34 2533  96  69   7 0.02
Fri 06/19 05Z 1.21 2632  97  67   7 0.02
Fri 06/19 06Z 1.15 2632  96  67   7 0.02
Fri 06/19 07Z 0.98 2632  95  69   8 0.01
Fri 06/19 08Z 0.94 2633  93  70   8 0.01
Fri 06/19 09Z 0.91 2634  92  70   8 0.01
Fri 06/19 10Z 0.92 2634  93  63   8 0.01
Fri 06/19 11Z 0.90 2633  93  64   9 0.01
Fri 06/19 12Z 0.92 2632  93  61   9 0.01
Fri 06/19 13Z 0.99 2632  93  60   9 0.01
Fri 06/19 14Z 1.10 2630  92  54   8 0.01
Fri 06/19 15Z 1.17 2629  89  49   9 0.01
Fri 06/19 16Z 1.76 2528  89  48   9 0.00
Fri 06/19 17Z 3.75 2528  89  51   8 0.00

Run total areal avg QPF for the greens is: 1.37 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