NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260831_1200
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)
=== ===== === ==== ==== === === === ====
Mon 08/31 12Z 0.12 3206  81   5   9 0.00
Mon 08/31 13Z 0.12 3105  80   6   9 0.00
Mon 08/31 14Z 0.11 3104  79   5  10 0.00
Mon 08/31 15Z 0.11 3003  78   3  10 0.00
Mon 08/31 16Z 0.13 2803  78   1  10 0.00
Mon 08/31 17Z 0.20 2703  76   0  10 0.00
Mon 08/31 18Z 0.29 2604  73   0  10 0.00
Mon 08/31 19Z 0.46 2604  70   8  10 0.00
Mon 08/31 20Z 0.38 2603  66  22  11 0.00
Mon 08/31 21Z 0.31 2504  65  32  11 0.00
Mon 08/31 22Z 0.25 2504  64  46  11 0.00
Mon 08/31 23Z 0.18 2404  65  67  11 0.00
Tue 09/01 00Z 0.13 2403  64  79  12 0.00
Tue 09/01 01Z 0.11 2303  66  83  11 0.00
Tue 09/01 02Z 0.08 2103  68  85  11 0.00
Tue 09/01 03Z 0.05 1903  71  85  12 0.00
Tue 09/01 04Z 0.05 1903  74  85  12 0.00
Tue 09/01 05Z 0.02 1803  75  83  12 0.00
Tue 09/01 06Z 0.03 1703  77  83  12 0.00
Tue 09/01 07Z 0.08 1504  80  86  12 0.00
Tue 09/01 08Z 0.12 1405  83  89  12 0.01
Tue 09/01 09Z 0.18 1308  86  88  12 0.01
Tue 09/01 10Z 0.20 1410  89  89  12 0.01
Tue 09/01 11Z 0.20 1411  88  81  12 0.01
Tue 09/01 12Z 0.22 1413  88  84  12 0.01
Tue 09/01 13Z 0.25 1416  88  90  12 0.01
Tue 09/01 14Z 0.25 1418  90  94  12 0.04
Tue 09/01 15Z 0.25 1518  93  94  12 0.13
Tue 09/01 16Z 0.29 1318  95  91  12 0.09
Tue 09/01 17Z 0.35 1319  95  97  12 0.14
Tue 09/01 18Z 0.47 1222  93  97  12 0.22
Tue 09/01 19Z 0.56 1124  93  96  11 0.21
Tue 09/01 20Z 0.58 1124  93  97  10 0.26
Tue 09/01 21Z 0.55 1124  92  95  11 0.09
Tue 09/01 22Z 0.53 1225  91  92  11 0.03
Tue 09/01 23Z 0.52 1328  92  91  11 0.01
Wed 09/02 00Z 0.51 1329  92  86  11 0.01
Wed 09/02 01Z 0.52 1329  92  80  10 0.01
Wed 09/02 02Z 0.50 1329  91  78  10 0.01
Wed 09/02 03Z 0.47 1327  89  75  10 0.01
Wed 09/02 04Z 0.45 1327  88  72  10 0.01
Wed 09/02 05Z 0.40 1325  87  71  10 0.01
Wed 09/02 06Z 0.34 1423  86  68  11 0.01
Wed 09/02 07Z 0.33 1322  82  64  11 0.01
Wed 09/02 08Z 0.32 1321  78  61  10 0.00
Wed 09/02 09Z 0.29 1420  75  60  10 0.00
Wed 09/02 10Z 0.26 1418  73  58  10 0.00
Wed 09/02 11Z 0.27 1318  71  55  11 0.00
Wed 09/02 12Z 0.26 1418  71  53  10 0.00
Wed 09/02 13Z 0.21 1417  72  54  10 0.00
Wed 09/02 14Z 0.17 1518  74  52  10 0.00
Wed 09/02 15Z 0.14 1617  75  48  10 0.00
Wed 09/02 16Z 0.09 1616  77  43  10 0.00
Wed 09/02 17Z 0.08 1614  79  36  10 0.00
Wed 09/02 18Z 0.09 1613  81  31  10 0.00
Wed 09/02 19Z 0.07 1712  84  43  10 0.00
Wed 09/02 20Z 0.05 1712  88  43   9 0.00
Wed 09/02 21Z 0.09 1712  89  51  10 0.00
Wed 09/02 22Z 0.09 1615  89  57  11 0.00
Wed 09/02 23Z 0.06 1717  90  77  12 0.00

Run total areal avg QPF for the greens is: 1.36 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