Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260219_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 02/19 06Z 0.21 0312  56  17  -6 0.00
Thu 02/19 07Z 0.30 0413  55   9  -6 0.00
Thu 02/19 08Z 0.21 0509  46   4  -6 0.00
Thu 02/19 09Z 0.14 0406  36   2  -5 0.00
Thu 02/19 10Z 0.12 0406  33   2  -5 0.00
Thu 02/19 11Z 0.13 0406  33   4  -5 0.00
Thu 02/19 12Z 0.10 0504  31   5  -5 0.00
Thu 02/19 13Z 0.10 0704  29   5  -4 0.00
Thu 02/19 14Z 0.06 0802  28   6  -4 0.00
Thu 02/19 15Z 0.06 0802  27   6  -4 0.00
Thu 02/19 16Z 0.05 0902  29   7  -4 0.00
Thu 02/19 17Z 0.06 1002  32   9  -4 0.00
Thu 02/19 18Z 0.02 1502  38  15  -4 0.00
Thu 02/19 19Z 0.02 1603  43  25  -4 0.00
Thu 02/19 20Z 0.07 1903  49  39  -5 0.00
Thu 02/19 21Z 0.13 2105  53  54  -4 0.00
Thu 02/19 22Z 0.14 2106  52  61  -4 0.00
Thu 02/19 23Z 0.13 2206  47  45  -3 0.00
Fri 02/20 00Z 0.12 2205  48  34  -3 0.00
Fri 02/20 01Z 0.08 2104  55  26  -3 0.00
Fri 02/20 02Z 0.08 2005  64  27  -4 0.00
Fri 02/20 03Z 0.14 2007  74  28  -4 0.00
Fri 02/20 04Z 0.20 2109  82  28  -5 0.00
Fri 02/20 05Z 0.27 2211  87  28  -5 0.00
Fri 02/20 06Z 0.18 2209  88  22  -3 0.00
Fri 02/20 07Z 0.19 2210  90  20  -3 0.00
Fri 02/20 08Z 0.15 2208  88  18  -2 0.00
Fri 02/20 09Z 0.13 2207  86  16  -2 0.00
Fri 02/20 10Z 0.05 1904  85  20  -2 0.00
Fri 02/20 11Z 0.03 1805  85  24  -2 0.00
Fri 02/20 12Z 0.03 1707  85  28  -2 0.00
Fri 02/20 13Z 0.02 1707  83  30  -2 0.00
Fri 02/20 14Z 0.03 1609  79  24  -2 0.00
Fri 02/20 15Z 0.02 1711  78  24  -2 0.00
Fri 02/20 16Z 0.02 1612  78  25  -2 0.00
Fri 02/20 17Z 0.04 1713  78  35  -2 0.00
Fri 02/20 18Z 0.03 1714  79  76  -2 0.00
Fri 02/20 19Z 0.05 1514  90  93  -1 0.01
Fri 02/20 20Z 0.11 1417  95  96   0 0.04
Fri 02/20 21Z 0.15 1420  96  98   0 0.03
Fri 02/20 22Z 0.18 1421  96  98   0 0.05
Fri 02/20 23Z 0.21 1422  95  98  -1 0.10
Sat 02/21 00Z 0.22 1322  95  99  -1 0.15
Sat 02/21 01Z 0.26 1323  95  98  -2 0.09
Sat 02/21 02Z 0.30 1323  96  97  -3 0.07
Sat 02/21 03Z 0.31 1321  96  97  -4 0.05
Sat 02/21 04Z 0.34 1320  95  95  -6 0.06
Sat 02/21 05Z 0.33 1419  95  85  -7 0.03
Sat 02/21 06Z 0.22 1517  95  93  -7 0.03
Sat 02/21 07Z 0.07 1615  94  95  -7 0.03
Sat 02/21 08Z 0.06 1714  94  96  -7 0.02
Sat 02/21 09Z 0.10 1812  95  95  -7 0.02
Sat 02/21 10Z 0.14 1812  97  96  -7 0.02
Sat 02/21 11Z 0.14 1911  98  95  -7 0.02
Sat 02/21 12Z 0.14 1909  98  94  -7 0.02
Sat 02/21 13Z 0.18 2009  97  91  -7 0.03
Sat 02/21 14Z 0.20 2108  97  89  -7 0.03
Sat 02/21 15Z 0.22 2207  97  88  -7 0.02
Sat 02/21 16Z 0.26 2407  97  87  -7 0.01
Sat 02/21 17Z 0.24 2406  98  83  -7 0.01

Run total areal avg QPF for the Central_Greens is: 0.94 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