NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260821_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 08/21 18Z 0.83 3503  74   9  10 0.00
Fri 08/21 19Z 0.62 0003  74  10  10 0.00
Fri 08/21 20Z 0.40 0004  74  10  10 0.00
Fri 08/21 21Z 0.36 0104  74  11  10 0.00
Fri 08/21 22Z 0.43 0205  75  11  10 0.00
Fri 08/21 23Z 0.34 0405  75  10  10 0.00
Sat 08/22 00Z 0.35 0506  75   9  10 0.00
Sat 08/22 01Z 0.42 0707  75   8  10 0.00
Sat 08/22 02Z 0.48 0807  77   7  10 0.00
Sat 08/22 03Z 0.42 1007  78   6  10 0.00
Sat 08/22 04Z 0.34 1107  79   6  10 0.00
Sat 08/22 05Z 0.30 1207  78   5  10 0.00
Sat 08/22 06Z 0.24 1307  79   5  10 0.00
Sat 08/22 07Z 0.22 1407  80   6  10 0.00
Sat 08/22 08Z 0.24 1408  81   7  10 0.00
Sat 08/22 09Z 0.23 1509  81   8   9 0.00
Sat 08/22 10Z 0.26 1509  81   9   9 0.00
Sat 08/22 11Z 0.33 1410  81  10   9 0.00
Sat 08/22 12Z 0.40 1311  80  11   9 0.00
Sat 08/22 13Z 0.49 1313  78  12   9 0.00
Sat 08/22 14Z 0.59 1315  76  13   9 0.00
Sat 08/22 15Z 0.88 1215  76  13  10 0.00
Sat 08/22 16Z 1.59 1214  76  13  10 0.00
Sat 08/22 17Z 2.80 1212  77  13  10 0.00
Sat 08/22 18Z 3.87 1310  77  15  10 0.00
Sat 08/22 19Z 4.27 1310  78  19  10 0.00
Sat 08/22 20Z 3.27 1310  79  21  11 0.00
Sat 08/22 21Z 2.10 1410  81  23  11 0.00
Sat 08/22 22Z 1.12 1411  82  29  11 0.00
Sat 08/22 23Z 0.70 1412  82  33  11 0.00
Sun 08/23 00Z 0.41 1413  80  33  11 0.00
Sun 08/23 01Z 0.24 1412  80  33  12 0.00
Sun 08/23 02Z 0.19 1412  79  31  12 0.00
Sun 08/23 03Z 0.19 1412  79  35  12 0.00
Sun 08/23 04Z 0.16 1511  80  37  12 0.00
Sun 08/23 05Z 0.14 1511  79  40  12 0.00
Sun 08/23 06Z 0.14 1511  79  43  13 0.00
Sun 08/23 07Z 0.15 1512  81  51  12 0.00
Sun 08/23 08Z 0.15 1511  83  61  12 0.01
Sun 08/23 09Z 0.19 1412  86  70  12 0.01
Sun 08/23 10Z 0.22 1413  88  78  12 0.01
Sun 08/23 11Z 0.27 1315  90  83  13 0.01
Sun 08/23 12Z 0.26 1416  92  87  13 0.03
Sun 08/23 13Z 0.21 1517  94  90  13 0.10
Sun 08/23 14Z 0.18 1518  95  87  13 0.06
Sun 08/23 15Z 0.10 1618  97  82  13 0.05
Sun 08/23 16Z 0.14 1619  93  70  14 0.04
Sun 08/23 17Z 0.08 1719  96  69  14 0.01
Sun 08/23 18Z 0.05 1818  98  63  14 0.01
Sun 08/23 19Z 0.09 1816  98  64  14 0.01
Sun 08/23 20Z 0.15 1915  95  60  14 0.01
Sun 08/23 21Z 0.21 2015  91  51  14 0.00
Sun 08/23 22Z 0.27 2016  91  47  14 0.00
Sun 08/23 23Z 0.32 2018  93  33  14 0.00
Mon 08/24 00Z 0.42 2119  94  42  13 0.01
Mon 08/24 01Z 0.45 2316  85  64  13 0.10
Mon 08/24 02Z 0.45 2515  76  50  13 0.01
Mon 08/24 03Z 0.42 2514  74  52  13 0.00
Mon 08/24 04Z 0.35 2412  78  39  13 0.00
Mon 08/24 05Z 0.29 2311  74  33  13 0.00

Run total areal avg QPF for the greens is: 0.48 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