Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260310_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 03/10 06Z 1.07 2632  37  45   8 0.00
Tue 03/10 07Z 1.13 2632  37  49   8 0.00
Tue 03/10 08Z 1.11 2730  39  54   8 0.00
Tue 03/10 09Z 1.09 2828  43  56   7 0.00
Tue 03/10 10Z 0.91 2825  48  53   7 0.00
Tue 03/10 11Z 0.74 2822  52  50   7 0.00
Tue 03/10 12Z 0.60 2719  54  53   7 0.00
Tue 03/10 13Z 0.51 2617  53  55   8 0.00
Tue 03/10 14Z 0.48 2516  52  55   8 0.00
Tue 03/10 15Z 0.50 2418  50  48   8 0.00
Tue 03/10 16Z 0.55 2320  49  44   8 0.00
Tue 03/10 17Z 0.64 2420  51  43   8 0.00
Tue 03/10 18Z 0.72 2419  55  29   7 0.00
Tue 03/10 19Z 0.84 2418  62  34   7 0.00
Tue 03/10 20Z 0.94 2516  70  48   7 0.00
Tue 03/10 21Z 0.98 2516  79  45   6 0.00
Tue 03/10 22Z 0.83 2617  85  41   6 0.00
Tue 03/10 23Z 0.65 2617  89  39   6 0.00
Wed 03/11 00Z 0.50 2614  93  40   6 0.00
Wed 03/11 01Z 0.36 2612  95  43   6 0.01
Wed 03/11 02Z 0.25 2709  97  51   6 0.02
Wed 03/11 03Z 0.18 2707  97  60   6 0.01
Wed 03/11 04Z 0.13 2706  98  52   7 0.01
Wed 03/11 05Z 0.11 2605  98  65   7 0.02
Wed 03/11 06Z 0.08 2205  98  56   7 0.01
Wed 03/11 07Z 0.06 1907  98  57   7 0.01
Wed 03/11 08Z 0.04 1810  98  54   7 0.01
Wed 03/11 09Z 0.04 1716  98  54   7 0.01
Wed 03/11 10Z 0.08 1622  98  44   8 0.02
Wed 03/11 11Z 0.08 1728  98  50   8 0.03
Wed 03/11 12Z 0.06 1731  97  51   8 0.03
Wed 03/11 13Z 0.04 1732  97  46   9 0.02
Wed 03/11 14Z 0.08 1835  97  56   9 0.02
Wed 03/11 15Z 0.13 1937  96  58  10 0.02
Wed 03/11 16Z 0.17 1938  96  74  10 0.03
Wed 03/11 17Z 0.21 1939  96  63  10 0.04
Wed 03/11 18Z 0.22 1940  93  37  10 0.01
Wed 03/11 19Z 0.26 2043  94  27  10 0.01
Wed 03/11 20Z 0.26 2044  91  52  11 0.00
Wed 03/11 21Z 0.26 2043  90  83  12 0.01
Wed 03/11 22Z 0.26 1945  90  92  12 0.01
Wed 03/11 23Z 0.35 2047  94  93  11 0.05
Thu 03/12 01Z 0.44 2048  93  83  12 0.02
Thu 03/12 02Z 0.46 2047  92  80  12 0.01
Thu 03/12 03Z 0.41 2046  92  89  13 0.00
Thu 03/12 04Z 0.88 2243  96  96  11 0.00
Thu 03/12 05Z 0.87 2435  94  84   8 0.28
Thu 03/12 06Z 1.35 2438  98  56   5 0.24
Thu 03/12 07Z 1.65 2540  92  50   0 0.02
Thu 03/12 08Z 2.15 2541  93  38  -5 0.04
Thu 03/12 09Z 2.51 2539  94   6  -8 0.00
Thu 03/12 10Z 3.24 2638  94   5 -10 0.00
Thu 03/12 11Z 4.46 2640  93   3 -12 0.00
Thu 03/12 12Z 7.68 2739  92   6 -13 0.01
Thu 03/12 13Z 9.68 2736  92  10 -14 0.00
Thu 03/12 14Z 10.07 2735  88  15 -15 0.00
Thu 03/12 15Z 14.51 2832  87  21 -14 0.00
Thu 03/12 16Z 15.68 2830  82  29 -14 0.00
Thu 03/12 17Z 16.60 2827  80  36 -13 0.00

Run total areal avg QPF for the greens is: 1.03 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