Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260220_1800
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)
=== ===== === ==== ==== === === === ====
Fri 02/20 18Z 0.13 1515  81  70  -1 0.00
Fri 02/20 19Z 0.20 1418  83  78  -1 0.01
Fri 02/20 20Z 0.23 1419  87  87  -1 0.04
Fri 02/20 21Z 0.25 1420  90  94  -1 0.07
Sat 02/21 00Z 0.37 1221  95  97  -2 0.08
Sat 02/21 01Z 0.34 1319  96  93  -4 0.10
Sat 02/21 02Z 0.28 1416  96  94  -5 0.12
Sat 02/21 03Z 0.22 1515  95  92  -5 0.11
Sat 02/21 04Z 0.18 1513  95  90  -6 0.11
Sat 02/21 05Z 0.11 1610  95  91  -6 0.08
Sat 02/21 06Z 0.08 1608  96  91  -7 0.04
Sat 02/21 07Z 0.07 1707  96  89  -7 0.03
Sat 02/21 08Z 0.08 1806  96  91  -7 0.03
Sat 02/21 09Z 0.14 2006  97  93  -7 0.02
Sat 02/21 10Z 0.18 2305  97  92  -7 0.02
Sat 02/21 11Z 0.20 2605  98  90  -7 0.02
Sat 02/21 12Z 0.19 2905  98  88  -7 0.02
Sat 02/21 13Z 0.18 3005  98  89  -7 0.02
Sat 02/21 14Z 0.16 3106  99  88  -8 0.02
Sat 02/21 15Z 0.12 3305  98  82  -8 0.01
Sat 02/21 16Z 0.11 3505  97  76  -8 0.01
Sat 02/21 17Z 0.10 0005  93  68  -8 0.00
Sat 02/21 18Z 0.10 0105  88  62  -8 0.00
Sat 02/21 19Z 0.09 0105  83  59  -8 0.00
Sat 02/21 20Z 0.07 0105  80  50  -8 0.00
Sat 02/21 21Z 0.07 0205  77  44  -8 0.00
Sat 02/21 22Z 0.10 0306  74  39  -8 0.00
Sat 02/21 23Z 0.15 0407  72  37  -8 0.00
Sun 02/22 00Z 0.18 0508  67  38  -8 0.00
Sun 02/22 01Z 0.21 0609  61  33  -8 0.00
Sun 02/22 02Z 0.22 0809  60  29  -7 0.00
Sun 02/22 03Z 0.21 0908  62  27  -7 0.00
Sun 02/22 04Z 0.21 1008  60  27  -7 0.00
Sun 02/22 05Z 0.21 1109  55  27  -7 0.00
Sun 02/22 06Z 0.20 1209  54  28  -7 0.00
Sun 02/22 07Z 0.19 1310  54  29  -7 0.00
Sun 02/22 08Z 0.17 1311  53  29  -7 0.00
Sun 02/22 09Z 0.16 1411  50  29  -7 0.00
Sun 02/22 10Z 0.17 1311  50  29  -7 0.00
Sun 02/22 11Z 0.21 1312  52  28  -7 0.00
Sun 02/22 12Z 0.23 1313  55  27  -7 0.00
Sun 02/22 13Z 0.27 1214  58  27  -7 0.00
Sun 02/22 14Z 0.26 1314  61  30  -7 0.00
Sun 02/22 15Z 0.26 1315  62  36  -7 0.00
Sun 02/22 16Z 0.29 1314  62  36  -7 0.00
Sun 02/22 17Z 0.32 1214  62  35  -7 0.00
Sun 02/22 18Z 0.36 1214  65  37  -7 0.00
Sun 02/22 19Z 0.40 1214  70  37  -7 0.00
Sun 02/22 20Z 0.44 1213  75  36  -7 0.00
Sun 02/22 21Z 0.46 1113  76  35  -7 0.00
Sun 02/22 22Z 0.46 1114  76  40  -7 0.00
Sun 02/22 23Z 0.47 1014  71  39  -7 0.00
Mon 02/23 00Z 0.49 1016  68  42  -7 0.00
Mon 02/23 01Z 0.50 0917  64  46  -7 0.00
Mon 02/23 02Z 0.47 1018  53  39  -7 0.00
Mon 02/23 03Z 0.46 1020  47  40  -7 0.00
Mon 02/23 04Z 0.48 0921  43  38  -7 0.00
Mon 02/23 05Z 0.50 0922  40  37  -7 0.00

Run total areal avg QPF for the greens is: 0.96 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