NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260831_1200
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)
=== ===== === ==== ==== === === === ====
Mon 08/31 12Z 0.04 3305  80   2  10 0.00
Mon 08/31 13Z 0.06 3204  78   3  10 0.00
Mon 08/31 14Z 0.06 3103  76   3  10 0.00
Mon 08/31 15Z 0.07 3002  75   1  10 0.00
Mon 08/31 16Z 0.09 2702  76   0  10 0.00
Mon 08/31 17Z 0.19 2602  75   0  10 0.00
Mon 08/31 18Z 0.31 2503  72   0  11 0.00
Mon 08/31 19Z 0.53 2503  69   9  11 0.00
Mon 08/31 20Z 0.43 2503  66  25  11 0.00
Mon 08/31 21Z 0.36 2504  66  35  11 0.00
Mon 08/31 22Z 0.28 2405  68  51  12 0.00
Mon 08/31 23Z 0.19 2404  69  80  12 0.00
Tue 09/01 00Z 0.13 2303  68  94  12 0.00
Tue 09/01 01Z 0.11 2203  71  96  12 0.00
Tue 09/01 02Z 0.10 2004  75  97  12 0.00
Tue 09/01 03Z 0.08 1904  79  97  12 0.00
Tue 09/01 04Z 0.07 1904  82  96  12 0.00
Tue 09/01 05Z 0.04 1804  84  96  12 0.00
Tue 09/01 06Z 0.03 1704  86  96  12 0.00
Tue 09/01 07Z 0.05 1505  88  96  12 0.01
Tue 09/01 08Z 0.10 1406  92  97  12 0.01
Tue 09/01 09Z 0.17 1309  94  97  12 0.01
Tue 09/01 10Z 0.17 1411  96  95  12 0.01
Tue 09/01 11Z 0.17 1412  95  88  12 0.01
Tue 09/01 12Z 0.19 1414  95  93  12 0.01
Tue 09/01 13Z 0.18 1417  96  97  13 0.02
Tue 09/01 14Z 0.15 1520  98  99  13 0.06
Tue 09/01 15Z 0.12 1519  98  97  13 0.14
Tue 09/01 16Z 0.16 1419  98  90  13 0.06
Tue 09/01 17Z 0.23 1420  98  99  13 0.10
Tue 09/01 18Z 0.37 1222  98  99  12 0.27
Tue 09/01 19Z 0.48 1124  97  97  11 0.30
Tue 09/01 20Z 0.59 1025  96  98  10 0.38
Tue 09/01 21Z 0.57 1125  94  95  10 0.12
Tue 09/01 22Z 0.52 1127  94  91  11 0.03
Tue 09/01 23Z 0.51 1231  93  89  11 0.01
Wed 09/02 00Z 0.49 1231  92  81  11 0.01
Wed 09/02 01Z 0.49 1231  93  74  10 0.01
Wed 09/02 02Z 0.47 1230  93  73  10 0.01
Wed 09/02 03Z 0.44 1329  92  72  10 0.01
Wed 09/02 04Z 0.42 1328  91  71  10 0.01
Wed 09/02 05Z 0.37 1326  89  68  10 0.01
Wed 09/02 06Z 0.32 1323  86  67  10 0.01
Wed 09/02 07Z 0.30 1322  84  68  10 0.01
Wed 09/02 08Z 0.29 1322  79  67  10 0.01
Wed 09/02 09Z 0.26 1321  76  69  10 0.00
Wed 09/02 10Z 0.23 1319  75  67  10 0.00
Wed 09/02 11Z 0.25 1319  73  59  10 0.00
Wed 09/02 12Z 0.23 1319  74  55  10 0.00
Wed 09/02 13Z 0.19 1418  74  55  10 0.00
Wed 09/02 14Z 0.14 1518  77  50  10 0.00
Wed 09/02 15Z 0.10 1517  77  42  10 0.00
Wed 09/02 16Z 0.05 1615  78  33  10 0.00
Wed 09/02 17Z 0.04 1613  81  26  10 0.00
Wed 09/02 18Z 0.05 1612  84  27  10 0.00
Wed 09/02 19Z 0.02 1611  87  46   9 0.00
Wed 09/02 20Z 0.06 1711  90  44   9 0.00
Wed 09/02 21Z 0.07 1611  90  51  10 0.00
Wed 09/02 22Z 0.06 1613  90  63  11 0.00
Wed 09/02 23Z 0.03 1615  90  78  12 0.00

Run total areal avg QPF for the Central_Greens is: 1.64 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