NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260821_1800
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)
=== ===== === ==== ==== === === === ====
Fri 08/21 18Z 0.90 0103  74  10  10 0.00
Fri 08/21 19Z 0.87 0103  74  10  11 0.00
Fri 08/21 20Z 0.66 0104  76  10  11 0.00
Fri 08/21 21Z 0.62 0204  76  11  11 0.00
Fri 08/21 22Z 0.71 0305  77  10  10 0.00
Fri 08/21 23Z 0.50 0406  78  10  10 0.00
Sat 08/22 00Z 0.43 0507  78  10  10 0.00
Sat 08/22 01Z 0.49 0708  78   8  10 0.00
Sat 08/22 02Z 0.53 0808  80   7  10 0.00
Sat 08/22 03Z 0.43 0908  82   5  10 0.00
Sat 08/22 04Z 0.33 1107  83   4  10 0.00
Sat 08/22 05Z 0.29 1207  81   4  10 0.00
Sat 08/22 06Z 0.22 1307  80   4  10 0.00
Sat 08/22 07Z 0.21 1308  80   5  10 0.00
Sat 08/22 08Z 0.25 1309  81   6  10 0.00
Sat 08/22 09Z 0.26 1409  81   7  10 0.00
Sat 08/22 10Z 0.29 1310  81   8   9 0.00
Sat 08/22 11Z 0.39 1211  79  10   9 0.00
Sat 08/22 12Z 0.49 1113  79  12   9 0.00
Sat 08/22 13Z 0.54 1115  75  13   9 0.00
Sat 08/22 14Z 0.60 1117  73  14  10 0.00
Sat 08/22 15Z 0.68 1116  72  13  10 0.00
Sat 08/22 16Z 0.97 1115  73  13  10 0.00
Sat 08/22 17Z 2.14 1213  75  13  10 0.00
Sat 08/22 18Z 3.74 1211  76  17  10 0.00
Sat 08/22 19Z 4.22 1211  79  20  10 0.00
Sat 08/22 20Z 2.83 1310  82  21  11 0.00
Sat 08/22 21Z 1.43 1310  85  23  11 0.00
Sat 08/22 22Z 0.61 1311  86  30  11 0.00
Sat 08/22 23Z 0.40 1312  86  31  11 0.00
Sun 08/23 00Z 0.26 1312  83  30  11 0.00
Sun 08/23 01Z 0.17 1412  82  31  12 0.00
Sun 08/23 02Z 0.14 1412  82  30  12 0.00
Sun 08/23 03Z 0.15 1412  82  36  12 0.00
Sun 08/23 04Z 0.12 1411  83  40  12 0.00
Sun 08/23 05Z 0.11 1411  81  43  13 0.00
Sun 08/23 06Z 0.10 1411  80  47  13 0.00
Sun 08/23 07Z 0.11 1513  84  59  12 0.01
Sun 08/23 08Z 0.11 1512  86  74  12 0.01
Sun 08/23 09Z 0.15 1412  89  84  12 0.01
Sun 08/23 10Z 0.19 1314  92  87  12 0.01
Sun 08/23 11Z 0.23 1316  95  87  12 0.01
Sun 08/23 12Z 0.20 1416  95  92  13 0.04
Sun 08/23 13Z 0.15 1417  96  92  13 0.16
Sun 08/23 14Z 0.11 1519  96  86  13 0.09
Sun 08/23 15Z 0.03 1618  97  83  13 0.05
Sun 08/23 16Z 0.05 1619  93  70  15 0.05
Sun 08/23 17Z 0.06 1720  96  67  14 0.01
Sun 08/23 18Z 0.13 1818  99  58  14 0.01
Sun 08/23 19Z 0.20 1916  98  62  14 0.01
Sun 08/23 20Z 0.27 2014  93  60  14 0.00
Sun 08/23 21Z 0.32 2114  90  45  14 0.00
Sun 08/23 22Z 0.39 2015  94  39  14 0.00
Sun 08/23 23Z 0.46 2017  95  24  13 0.01
Mon 08/24 00Z 0.52 2117  96  48  13 0.01
Mon 08/24 01Z 0.50 2415  83  64  13 0.14
Mon 08/24 02Z 0.48 2515  72  41  13 0.01
Mon 08/24 03Z 0.45 2514  75  50  13 0.00
Mon 08/24 04Z 0.40 2413  83  40  12 0.00
Mon 08/24 05Z 0.34 2312  78  26  13 0.00

Run total areal avg QPF for the Central_Greens is: 0.64 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